Continuous process for converting natural gas to liquid hydrocarbons

ABSTRACT

A method comprising: providing an alkyl halide stream; contacting at least some of the alkyl halides with a coupling catalyst to form a product stream comprising higher hydrocarbons and hydrogen halide; contacting the product stream with a solid reactant to remove at least a portion of the hydrogen halide from the product stream; and reacting the solid reactant with a source of oxygen to generate a corresponding halogen.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/504,894, filed Jul. 17, 2009, which is based on and claims priorityto U.S. Provisional Patent Application No. 61/081,976, filed Jul. 18,2008, U.S. Provisional Patent Application No. 61/082,000, filed Jul. 18,2008, U.S. Provisional Patent Application No. 61/082,115, filed Jul. 18,2008, U.S. Provisional Patent Application No. 61/082,143, filed Jul. 18,2008, and U.S. patent application Ser. No. 12/496,348, filed Jul. 1,2009 which is a continuation of Ser. No. 11/703,358 filed Feb. 5, 2007,the entire contents of each provisional and application are incorporatedby reference herein.

FIELD OF THE INVENTION

This invention generally relates to carbon-carbon coupling and, moreparticularly, to methods for converting hydrocarbon feedstocks intouseful products.

BACKGROUND OF THE INVENTION

Scientists have long sought efficient ways to convert methane and otherhydrocarbons into longer chain hydrocarbons, olefins, aromatichydrocarbons, and other products. CH bond activation has been the focusof intense research for decades, with mixed results. More efficientprocesses may create value in a number of ways, including facilitatingthe utilization of remotely located hydrocarbon feedstocks (such asstranded natural gas) through conversion into more easily transportableand useful fuels and feedstocks, and allowing the use of inexpensivefeedstocks (e.g., methane and other light hydrocarbons) for end productsoften made from higher hydrocarbons.

U.S. Pat. No. 6,525,230 discloses methods of converting alkanes to othercompounds using a “zone reactor” comprised of a hollow, unsegregatedinterior defining first, second, and third zones. Oxygen reacts withmetal bromide in the first zone to provide bromine; bromine reacts withthe alkane in the second zone to form alkyl bromide and hydrogenbromide; and the alkyl bromide reacts with metal oxide in the third zoneto form the corresponding product. In one embodiment, the flow of gasesthrough the reactor may be reversed to convert the metal oxide back tometal bromide and to convert the metal bromide back to the metal oxide.The reactor may essentially operated in a cyclic mode.

Other processes may include an oxidative halogenation process forproducing alkyl halides from an alkane, hydrogen halide, and,preferably, oxygen, using a rare earth halide or oxyhalide catalyst. Ametal halide catalyst may also be used for oxidative halogenation ofalkanes. Oxidative halogenation, however, has several disadvantages,including the production of perhalogenated products and an unacceptablequantity of deep oxidation products (CO and CO₂).

Other processes include a bromine-based process for converting gaseousalkanes to liquid hydrocarbons. Several basic steps may be used,including (1) reacting bromine with alkanes to produce alkyl bromidesand hydrobromic acid (bromination), (2) reacting the alkyl bromide andhydrobromic acid product with a crystalline alumino-silicate catalyst toform higher molecular weight hydrocarbons and hydrobromic acid(coupling), (3) neutralizing the hydrobromic acid by reaction with anaqueous solution of partially oxidized metal bromide salts (as metaloxides/oxybromides/bromides) to produce a metal bromide salt and waterin an aqueous solution, or by reaction of the hydrobromic acid with airover a metal bromide catalyst, and (4) regenerating bromine by reactionof the metal bromide salt with oxygen to yield bromine and an oxidizedsalt. Potential drawbacks of the processes may include low methaneconversions; short space-times and the resulting potential for less than100% bromine conversion; wasteful overbromination of ethane, propane,and higher alkanes, resulting in the formation of dibromomethane andother polybrominated alkanes, which will likely form coke under thedisclosed reaction conditions; comparatively low alkyl bromideconversions; the need to separate the hydrocarbon product stream from anaqueous hydrohalic acid stream; and inadequate capture of halogen duringthe regeneration of the catalyst to remove halogen-containing coke. Inaddition, the proposed venting of this bromine-containing stream may beboth economically and environmentally unacceptable.

The process described above may also requires operation at relativelylow temperatures to prevent significant selectivity to methane. Oneresult may be incomplete conversion of alkyl bromide species and,because the process relies on stream splitting to recover products, aconsiderable amount of unconverted alkyl bromides may leave the processwith the products. This represents an unacceptable loss of bromine (asunconverted methyl bromide) and a reduced carbon efficiency.

The neutralization of hydrobromic acid by reaction with an aqueoussolution of partially oxidized metal bromide salts and subsequentreaction of the metal bromide salts formed with oxygen to yield bromineand an oxidized salt may also have a number of disadvantages. First, anycarbon dioxide present may form carbonates in the slurry, which may notbe regenerable. Second, the maximum temperature may be limited due topressure increases which are intolerable above approximately 200° C.,thus preventing complete recovery of halogen. Third, although the use ofredox-active metal oxides (e.g., oxides of V, Cr, Mn, Fe, Co, Ce, andCu) may contribute to molecular bromine formation during theneutralization of hydrobromic acid, incomplete HBr conversion due to theuse of a solid bromide salt may in turn result in a significant loss ofbromine from the system (in the water phase). Provided an excess of airwas used, the bromide salt might eventually be converted to the oxideform, stopping any further loss of HBr in the water discard.

To separate water from bromine, a process may utilize condensation andphase separation to produce semi-dry liquid bromine and a water/brominemixture. Other means for separating water from bromine, such as using aninert gas to strip the bromine from the water phase or usingadsorption-based methods have also been proposed; however, such methodsare minimally effective and result in a significant overall loss ofhalogen.

An oxychlorination process may first remove the water from HCl (a costlystep) and then reacts the HCl with oxygen and hydrocarbon directly.Oxychlorination processes rely on the separation of HCl from theunreacted alkanes and higher hydrocarbon products by using waterabsorption, and subsequent recovery of anhydrous HCl from the aqueoushydrochloric acid. Processes for the absorption of HCl in water maydissapate the heat of absorption by contacting the HCl gas with ambientair, and also by the vaporization of water. Such processes may produceaqueous hydrochloric acid with a concentration of at least 35.5 wt %.Other processes may allow for the recovery of anhydrous HCl gas byextractive distillation using a chloride salt. Still other processesallow for the production of gaseous HCl from dilute aqueous HCl using anamine together with an inert water-immiscible solvent.

Although researchers have made some progress in the search for moreefficient CH bond activation pathways for converting natural gas andother hydrocarbon feedstocks into fuels and other products, thereremains a tremendous need for a continuous, economically viable, andmore efficient process.

SUMMARY

This invention generally relates to carbon-carbon coupling and, moreparticularly, to methods for converting hydrocarbon feedstocks intouseful products.

An embodiment comprises a method comprising: providing an alkyl halidestream; contacting at least some of the alkyl halides with a couplingcatalyst to form a product stream comprising higher hydrocarbons andhydrogen halide; contacting the product stream with a solid reactant toremove at least a portion of the hydrogen halide from the productstream; and reacting the solid reactant with a source of oxygen togenerate a corresponding halogen.

Another embodiment comprises a method comprising: providing an alkylhalide stream; contacting at least some of the alkyl halides with acoupling catalyst to form a product stream comprising higherhydrocarbons and hydrogen halide; separating at least some of theproduct stream from the hydrogen halide; and contacting the hydrogenhalide with oxygen and an aqueous solution comprising a metal capable offorming multiple stable oxidation states to generate a correspondinghalogen and water.

Still another embodiment comprises a system comprising: a couplingreactor comprising a coupling catalyst for receiving an alkyl halidestream and contacting at least a portion of the alkyl halide stream withthe coupling catalyst to form a product stream comprising higherhydrocarbons and hydrogen halide; a separator unit for separating atleast some of the product stream from the hydrogen halide; and anoxidation reactor comprising an aqueous solution comprising a metalcapable of forming multiple stable oxidation states for receiving asource of oxygen and at least a portion of the hydrogen halide from theseparator unit and generating a corresponding halogen and water.

The features and advantages of the present invention will be apparent tothose skilled in the art. While numerous changes may be made by thoseskilled in the art, such changes are within the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one embodiment of a continuous process forconverting methane or natural gas into hydrocarbon chemicals accordingto the invention;

FIG. 2 is a schematic view of one embodiment of a continuous process forconverting methane or natural gas into hydrocarbon fuels according tothe invention;

FIG. 3 is a schematic view of one embodiment of a continuous process forconverting methane or natural gas into hydrocarbon fuels according tothe invention;

FIG. 4 is a schematic view of a subprocess for reproportionatingpolyhalides according to an alternate embodiment of the invention;

FIG. 5 is a schematic view of one embodiment of a continuous process fora halogenation reactor;

FIG. 6 is a schematic view of one embodiment of a monobromide separationcolumn, for use in the practice of the invention;

FIG. 7 is a schematic view of one embodiment of a catalytic couplingreactor with multiple catalytic beds;

FIG. 8 is another schematic view of one embodiment of a catalyticcoupling reactor with multiple catalytic beds;

FIG. 9 is a schematic view of one embodiment of an extractivedistillation system, for use in the practice of the invention;

FIG. 10 is a schematic view of one embodiment of a temperature swingabsorption system, for use in the practice of the invention;

FIG. 11 is a chart showing the solubility of HBr in water for oneembodiment of an absorption system, for use in the practice of theinvention;

FIG. 12 is a schematic view of one embodiment of a product separationsub-system, for use in the practice of the invention;

FIG. 13 is a chart showing the absorptive capacity of a NiO catalyst forone embodiment of an adsorption system, for use in the practice of theinvention;

FIG. 14 is a flow-chart showing one embodiment of a process for creatingsol-gel granules;

FIG. 15 is a flow-chart showing one embodiment of a process for creatingco-precipitation granules;

FIG. 16 is a schematic view of one embodiment of a liquid phase HBroxidation system, for use in the practice of the invention;

FIG. 17 is a schematic view of one embodiment of a product separationsub-system, for use in the practice of the invention;

FIG. 18 is a schematic view of one embodiment of a product separationsub-system, for use in the practice of the invention;

FIG. 19 is a schematic view of one embodiment of a product separationsub-system, for use in the practice of the invention;

FIG. 20 is a schematic view of one embodiment of a product separationsub-system, for use in the practice of the invention;

FIG. 21 is a schematic view of one embodiment of a product separationsub-system, for use in the practice of the invention;

FIG. 22 is a simplified block diagram of one embodiment of a continuousprocess for converting alkanes into hydrocarbon products according tothe invention, wherein water is separated from hydrocarbon products; and

FIG. 23 is a simplified block diagram of one embodiment of a continuousprocess for converting alkanes into hydrocarbon products according tothe invention, wherein water is separated after the alkane brominationstep.

FIG. 24 is a simplified block diagram of one embodiment of a continuousprocess for converting alkanes into hydrocarbon products according tothe invention, wherein a cataloreactant is used.

FIG. 25 is a schematic view of one embodiment of a continuous processfor converting methane or natural gas into hydrocarbon chemicalsaccording to the invention;

FIG. 26 is a simplified block diagram of one embodiment of a continuousprocess for converting alkanes into hydrocarbon products according tothe invention, wherein a copper bromine capture agent is used;

FIG. 27 is a schematic view of one embodiment of a continuous processfor converting methane or natural gas into hydrocarbon chemicalsaccording to the invention;

FIG. 28 is a schematic view of one embodiment of a continuous processfor converting methane or natural gas into hydrocarbon chemicalsaccording to the invention;

FIG. 29 is a schematic view of one embodiment of a continuous processfor converting methane or natural gas into hydrocarbon chemicalsaccording to the invention;

FIG. 30 is a schematic view of one embodiment of a continuous processfor converting methane or natural gas into hydrocarbon chemicalsaccording to the invention using a continuous flow zone reactorconfiguration;

FIG. 31 is a graph of bromobenzene conversion and benzene yield as afunction of time, for an experiment conducted according to oneembodiment of the invention; and

FIG. 32 is a graph of catalyst effectiveness as a function of time, foran experiment conducted according to one embodiment of the invention.

FIG. 33 is a graph of methyl bromide coupling results as a function oftemperature, for an experiment conducted according to one embodiment ofthe invention.

FIG. 34 is another graph of methyl bromide coupling results as afunction of temperature, for an experiment conducted according to oneembodiment of the invention.

FIG. 35 is a graph of methane selectivity as a function of cycle number,for an experiment conducted according to one embodiment of theinvention.

FIG. 36 is a graph of conversion efficiency as a function of retentiontime, for an experiment conducted according to one embodiment of theinvention.

FIG. 37 is a graph of coke production, for an experiment conductedaccording to one embodiment of the invention.

DETAILED DESCRIPTION

This invention generally relates to carbon-carbon coupling and, moreparticularly, to methods for converting hydrocarbon feedstocks intouseful products.

The present invention provides a chemical process that enables naturalgas and other hydrocarbon feedstocks to be converted into highermolecular weight hydrocarbon products, using molecular halogen toactivate C—H bonds in the feedstock. According to one aspect of theinvention, a continuous process for converting a hydrocarbon feedstockinto one or more higher hydrocarbons may comprise the steps of (a)forming alkyl halides by reacting molecular halogen with a hydrocarbonfeedstock (preferably a feedstock containing methane), under processconditions sufficient to form alkyl halides and hydrogen halide, wherebysubstantially all of the molecular halogen is consumed; (b) contactingthe reproportionated alkyl halides with a first catalyst under processconditions sufficient to form higher hydrocarbons and additionalhydrogen halide; (c) separating the higher hydrocarbons from thehydrogen halide; (d) regenerating molecular halogen under processconditions sufficient to form molecular halogen and water; and (e)repeating steps (a) through (d) a desired number of times. These stepscan be carried out in the order presented or, alternatively, in adifferent order.

In each of the aspects and embodiments of the invention, it is intendedthat the alkyl halides formed in step (a) can be all the same (e.g.,100% bromomethane) or, more typically, different (e.g., mixtures ofbromomethane, dibromomethane, dibromoethane, etc). Similarly, it iscontemplated that the “higher hydrocarbons” formed in step (b) can beall the same (e.g., 100% isooctane) or, more typically, different (e.g.,mixtures of aliphatic and/or aromatic compounds). As used herein, theterm “higher hydrocarbons” refers to hydrocarbons having a greaternumber of carbon atoms than one or more components of the hydrocarbonfeedstock, as well as olefinic hydrocarbons having the same or a greaternumber of carbon atoms as one or more components of the hydrocarbonfeedstock. For instance, if the feedstock is natural gas—typically amixture of light hydrocarbons, predominately methane, with lesseramounts of ethane, propane, and butane, and even smaller amounts oflonger chain hydrocarbons such as pentane, hexane, etc.—the “higherhydrocarbon(s)” produced according to the invention can include a C₂ orhigher hydrocarbon, such as ethane, propane, butane, C₅₊ hydrocarbons,aromatic hydrocarbons, etc., and optionally ethylene, propylene, and/orlonger olefins The term “light hydrocarbons” (sometimes abbreviated“LHCs”) refers to C₁-C₄ hydrocarbons, e.g., methane, ethane, propane,ethylene, propylene, butanes, and butenes, all of which are normallygases at room temperature and atmospheric pressure.

Nonlimiting examples of hydrocarbon feedstocks appropriate for use inthe present invention include alkanes, e.g., methane, ethane, propane,and even larger alkanes; olefins; natural gas and other mixtures ofhydrocarbons. In most cases, the feedstock will be primarily aliphaticin nature. Certain oil refinery processes yield light hydrocarbonstreams (so-called “light-ends,” typically a mixture of C₁-C₃hydrocarbons), which may be used with or without added methane as thehydrocarbon feedstock in one embodiment of the invention.

Representative halogens include bromine (Br₂) and chlorine (Cl₂). It isalso contemplated that fluorine and iodine may be used, though notnecessarily with equivalent results. Some of the problems associatedwith fluorine may likely be addressed by using dilute streams offluorine (e.g., fluorine gas carried by helium, nitrogen, or otherdiluent). It is expected, however, that more vigorous reactionconditions will be required for alkyl fluorides to couple and formhigher hydrocarbons, due to the strength of the fluorine-carbon bond.Similarly, problems associated with iodine (such as the endothermicnature of certain iodine reactions) may likely be addressed by carryingout the halogenation and/or coupling reactions at higher temperaturesand/or pressures. The use of bromine or chlorine is preferred. Whilebromine and hydrogen bromide may be used in the descriptions containedherein, it should be understood that chlorine, fluorine, or iodine maybe substituted unless otherwise specifically stated.

FIGS. 1 and 2 schematically illustrate two nonlimiting embodiments of aprocess according to the invention, with FIG. 1 depicting a process formaking hydrocarbon chemicals (e.g., benzene, toluene, xylenes, otheraromatic compounds, etc.), and FIG. 2 depicting a process for makingfuel-grade hydrocarbons, e.g., hydrocarbons comprising a predominantamount of C₅ and higher aliphatic hydrocarbons and (optionally) aromatichydrocarbons. The primary difference in the two embodiments is that theprocess depicted in FIG. 2 lacks the first separation unit (SEP I) anddoes not return polybrominated species to the bromination reactor for“reproportionation.” In the scheme shown in FIG. 2, the amount ofpolybromides produced may be reduced significantly by introducing lightgasses into the bromination reactor. The polybromides (from methanebromination) may react with the light gasses to form monobromoalkanes.For convenience, the figures depict a bromine-based process. Inalternate embodiments of the invention, however, chlorine or otherhalogens may be used.

As shown in FIG. 1, natural gas (or another hydrocarbon feedstock) andmolecular bromine may be carried by separate lines 1, 2 into a heatedbromination reactor 3 and allowed to react. Products (HBr, alkylbromides, optionally olefins), and possibly unreacted hydrocarbons, exitthe reactor and are carried by a line 4 into a first separation unit 5(SEP I), where monobrominated hydrocarbons and HBr may be separated frompolybrominated hydrocarbons. The polybromides may be carried by a line 6back to the bromination reactor, where they may undergo“reproportionation” with methane and/or other light hydrocarbons, whichmay be present in the natural gas and/or introduced to the brominationreactor as described below.

Reproportionation of the polybromides formed during the brominationreaction enriches the outlet stream with monobromides and olefinicspecies, and reduces the amount of polybrominated hydrocarbons thatenter the coupling reactor. This, in turn, may reduce the amount of cokethat forms during the carbon-carbon coupling reactions. For large scaleproduction of aromatic hydrocarbons, it may be possible to employadditional separation units, which may further purify the feed stream tothe coupling reactor by separating and recycling the polybromides,thereby reducing the amount of coke and the overall bromine requirement.

Unreacted hydrocarbon feedstock, HBr, monobromides, and (optionally)olefins formed in the bromination reactor may be carried by a line 7,through a heat exchanger 8, and enter a heated coupling reactor 9, wherethe monobromides (and, optionally, any olefins present) may react in thepresence of a coupling catalyst to form higher hydrocarbons. HBr, higherhydrocarbons, and (possibly) unreacted hydrocarbons and alkyl bromidesmay exit the coupling reactor and be carried by a line 10, throughanother heat exchanger 11, and enter an HBr absorption unit 12. Watermay be introduced into the unit through a separate line 13. HBr may beabsorbed in this unit, which may be a packed column or other gas-liquidcontacting device. The effluent, containing liquid hydrocarbons andaqueous HBr, may be carried by a line 14 to a liquid-liquid splitter 15,which phase-separates liquid hydrocarbons from the aqueous HBr stream.The liquid hydrocarbon products may then be carried by a line 16 to aproduct clean-up unit 17 to yield final hydrocarbon products.

After HBr is separated from the hydrocarbon products and unreactedmethane (and any other light hydrocarbons that may be present) in theHBr absorption unit, the methane (and other light hydrocarbons, if any)may be carried by a line 18 into a second separation unit 19 (SEP II),which employs pressure- or temperature-swing absorption, membrane-basedseparation, cryogenic distillation (preferable for large scaleproduction), or another suitable separation technology. Methane, andpossibly other light hydrocarbons, may be returned to the brominationreactor via one or more lines 20, 21. In the embodiment shown, methanemay be directed to an upstream region or “zone” of the brominationreactor, while other light hydrocarbons may be directed to a mid- ordownstream zone of the reactor (the latter to facilitatereproportionation of polybromides).

The aqueous HBr stream that evolves from the liquid-liquid splitter maybe carried by a line 22 to a bromine generation unit 23. Oxygen, air, oroxygen-enriched gas may also be fed into the unit through a separateline 24. Bromine may be regenerated by reacting HBr with oxygen in thepresence of a suitable catalyst. The resulting stream may contain water,molecular bromine, oxygen, nitrogen if air was used as the source ofoxygen, and possibly other gases. This product stream may be carried bya line 25 through a heat exchanger 26 into a flash vaporization unit 27,which separates most of the molecular bromine from water, oxygen,nitrogen, and other gases (if any) that are present. Molecular bromine,either as a liquid or vapor and containing no more than a trace of H₂O,may be carried by a line 28 to a heat exchanger 29, and then returned tothe bromination reactor.

Water from the flash vaporization unit containing up to about 3 wt % ofmolecular bromine may be sent by a line 30 to a distillation unit 31,which yields water as the bottoms stream and bromine or bromine-waterazeotrope as a distillate. The distillate may be returned through a line32 back to the flash vaporization unit.

The gaseous products of the flash vaporization unit (e.g., oxygen,nitrogen, optionally other gases, and no more than a minor or traceamount of bromine) may be carried by a line 33 to a bromine scavengingunit 34, which separates molecular bromine from the other gases. Therecovered bromine may then be carried by a line 35 through a heatexchanger 29 and reintroduced into the bromination reactor. The amountof bromine entering the scavenger may be further reduced by increasingthe amount of bromine recovered in the flash step by employing brinesolutions and direct contact cooling to allow the use of temperaturesbelow 0° C. The other gases (e.g., nitrogen, oxygen) may be vented tothe atmosphere.

In another embodiment, shown in FIG. 3, an HBr capture and oxidationscheme may be used to capture HBr from the products stream without usingaqueous absorption and regenerate elemental bromine. In this embodiment,the products stream exiting the coupling reactor 49 may pass through avessel 55 containing a solid reactant material. The solid reactant mayreact with the HBr to form a corresponding metal bromide and water,which may pass through the vessel along with the unaffected hydrocarbonproducts from the coupling reactor. The metal bromide 56 may then becontacted with air or oxygen 58 to regenerate the original solidreactant material 63 and an elemental bromine stream 59, which can berecycled for use in the bromination reactor 43.

Various embodiments and features of individual subprocesses and otherimprovements for carrying out the invention will now be described inmore detail.

Bromination

Bromination of the hydrocarbon feedstock may be carried out in a fixedbed, fluidized bed, or other suitable reactor, at a temperature andpressure such that the bromination products and reactants are gases, forexample, about 1 to about 50 atm, about 150° C. to about 600° C., morepreferably about 400° C. to about 600° C., even more preferably, about450° C. to about 515° C., with a residence time of about 1 to about 60seconds, more preferably about 1 to about 15 seconds. Highertemperatures tend to favor coke formation, while low temperaturesrequire larger reactors. Using a fluidized bed may offer the advantageof improved heat transfer.

Alkane bromination may be initiated using heat or light, with thermalmeans being preferred. In one embodiment, the reactor may also contain ahalogenation catalyst, such as a zeolite, amorphous alumino-silicate,acidic zirconia, tungstates, solid phosphoric acids, metal oxides, mixedmetal oxides, metal halides, mixed metal halides (the metal in suchcases being, e.g., nickel, copper, cerium, cobalt, etc.), and/or orother catalysts as described, e.g., in U.S. Pat. Nos. 3,935,289 and4,971,664, which are incorporated herein in their entirety. In analternate embodiment, the reactor contains a porous or non-porous inertmaterial that provides sufficient surface area to retain coke formed inthe reactor and prevent it from escaping. The inert material may alsopromote the formation of polyhalogenated hydrocarbons, such astribromopropane. In still another embodiment, both a catalyst and aninert material are provided in the reactor. Optionally, the reactor maycontain different regions or zones to allow, in one or more zones,complete conversion of molecular bromine to produce alkyl bromides andhydrogen bromide.

The bromination reaction may also be carried out in the presence of anisomerization catalyst, such as a metal bromide (e.g., NaBr, KBr, CuBr,NiBr₂, MgBr₂, CaBr₂), metal oxide (e.g., SiO₂, ZrO₂, Al₂O₃), or metal(Pt, Pd, Ru, Ir, Rh) to help generate the desired brominated isomer(s).Since isomerization and bromination conditions are similar, thebromination and isomerization may be carried out in the same reactorvessel. Alternatively, a separate isomerization reactor may be utilized,located downstream of the bromination reactor and upstream of thecoupling reactor.

In an embodiment, a separate bromination reactor may be used tobrominate a light hydrocarbon stream. Light hydrocarbon bromination ofC₁-C₅ alkanes with bromine may occur at temperatures ranging from about150° C. to about 550° C., with the optimal temperature depending on thealkanes that are present and being brominated. In some embodiments, apolybrominated methane stream from an alkyl polybromide separator may beused to brominate the light hydrocarbon stream in the separatebromination reactor. Light hydrocarbon bromination may proceed morequickly at elevated pressures (e.g., about 2 bar to about 30 bar).Polybromides produced during lights bromination may be reproportionatedto monobromides by allowing longer residence times. Polybromides ofC₂-C₅ alkanes may react better and produce less coke in the couplingreactor than the C₁ polybromides.

Reproportionation

In some embodiments, a key feature of the invention is the“reproportionation” of polyhalogenated hydrocarbons (polyhalides), i.e.,halogenated hydrocarbons containing two or more halogen atoms permolecule. Monohalogenated alkanes (monohalides) created during thehalogenation reaction may be desirable as predominant reactant speciesfor subsequent coupling reactions and formation of higher molecularweight hydrocarbons. For certain product selectivities, polyhalogenatedalkanes may be desirable. Reproportionation allows a desired enrichmentof monohalides to be achieved by reacting polyhalogenated alkyl halideswith nonhalogenated alkanes, generally in the substantial absence ofmolecular halogens, to control the ratio of mono-to-polyhalogenatedspecies. For example, dibromomethane may be reacted with methane toproduce methyl bromide; dibromomethane may be reacted with propane toproduce methyl bromide and propyl bromide and/or propylene; and soforth.

Reactive reproportionation may be accomplished by allowing thehydrocarbon feedstock and/or recycled alkanes to react withpolyhalogenated species from the halogenation reactor, preferably in thesubstantial absence of molecular halogen. As a practical matter,substantially all of the molecular halogen entering the halogenationreactor is quickly consumed, forming mono- and polyhalides; thereforereproportionation of higher bromides may be accomplished simply byintroducing polybromides into a mid- or downstream region or “zone” ofthe halogenation reactor, optionally heated to a temperature thatdiffers from the temperature of the rest of the reactor.

Alternatively, reproportionation may be carried out in a separate“reproportionation reactor,” where polyhalides and unhalogenated alkanesare allowed to react, preferably in the substantial absence of molecularhalogen. FIG. 4 illustrates one such embodiment where, for clarity, onlysignificant system elements are shown. As in FIG. 1, natural gas oranother hydrocarbon feedstock and molecular bromine may be carried byseparate lines 1, 2 to a heated bromination reactor 3 and allowed toreact. Products (e.g., HBr, alkyl bromides) and possibly unreactedhydrocarbons, may exit the reactor and be carried by a line 4 into afirst separation unit 5, where monobrominated hydrocarbons and HBr areseparated from polybrominated hydrocarbons. The monobromides, HBr, andpossibly unreacted hydrocarbons may be carried by a line 7, through aheat exchanger 8, to a coupling reactor 9, and allowed to react, asshown in FIG. 1. The polybromides may be carried by a line 6 to areproportionation reactor 36. Additional natural gas or other alkanefeedstock may also be introduced into the reproportionation reactor, viaa line 37. Polybromides may react with unbrominated alkanes in thereproportionation reactor to form monobromides, which may be carried bya line 38 to the coupling reactor 9, after first passing through a heatexchanger.

In another embodiment of the invention (not shown), where thehydrocarbon feedstock comprises natural gas containing a considerableamount of C₂ and higher hydrocarbons, the “fresh” natural gas feed isintroduced directly into the reproportionation reactor, and recycledmethane (which passes through the reproportionation reactor unconverted)is carried back into the halogenation reactor.

Reproportionation may be thermally driven and/or facilitated by use of acatalyst. Nonlimiting examples of suitable catalysts include metaloxides, metal halides, and zeolites. U.S. Pat. No. 4,654,449,incorporated herein in its entirety, discloses the reproportionation ofpolyhalogenated alkanes with alkanes using an acidic zeolite catalyst.U.S. Pat. Nos. 2,979,541 and 3,026,361 disclose the use of carbontetrachloride as a chlorinating agent for methane, ethane, propane andtheir chlorinated analogues. All three patents are incorporated byreference herein in their entirety.

Reproportionation of C₁-C₅ alkanes with dibromomethane and/or otherpolybromides may occur at temperatures ranging from about 350° C. toabout 550° C., with the optimal temperature depending on thepolybromide(s) that are present and the alkane(s) being brominated. Inaddition, reproportionation may proceed more quickly at elevatedpressures (e.g., about 2 bar to about 30 bar). By achieving a highinitial methane conversion in the halogenation reactor, substantialamounts of di- and tribromomethane may be created; those species maythen be used as bromination reagents in the reproportionation step.Using di- and tribromomethane may allow for controlled bromination ofC₁-C₅ alkanes to monobrominated C₁-C₅ bromoalkanes and C₂-C₅ olefins.Reproportionation of di- and tribromomethane may facilitate high initialmethane conversion during bromination, which may reduce the methanerecycle flow rate and enrich the reactant gas stream with C₂-C₅monobromoalkanes and olefins that couple to liquid products over avariety of catalysts, including zeolites.

In another embodiment of the invention, reproportionation may be carriedout without first separating the polyhalides in a separation unit. Thismay be facilitated by packing the “reproportionation zone” with acatalyst, such as a zeolite, that allows the reaction to occur at areduced temperature. For example, although propane reacts withdibromomethane to form bromomethane and bromopropane (an example of“reproportionation”), the reaction does not occur at an appreciable rateat temperatures below about 500° C. The use of a zeolite may allowreproportionation to occur at a reduced temperature, enabling speciessuch as methane and ethane to be brominated in one zone of the reactor,and di-, tri-, and other polybromides to be reproportionated in anotherzone of the reactor.

Bromine Recovery During Decoking

Inevitably, coke formation will occur in the halogenation andreproportionation processes. If catalysts are used in the reactor(s) orreactor zone(s), the catalysts may be deactivated by the coke;therefore, periodic removal of the carbonaceous deposits may berequired. In addition, we have discovered that, within the coke that isformed, bromine may also be found, and it is highly desirable that thisbromine be recovered in order to minimize loss of bromine in the overallprocess, which is important for both economic and environmental reasons.

Several forms of bromides may be present: HBr, organic bromides such asmethyl bromide and dibromomethane, and molecular bromine. The inventionprovides means for recovering this bromine from the decoking process. Inone embodiment, a given reactor may be switched off-line and air oroxygen may be introduced to combust the carbon deposits and produce HBrfrom the residual bromine residues. The effluent gas may be added to theair (or oxygen) reactant stream fed to the bromine generation reactor,thereby facilitating complete bromine recovery. This process may berepeated periodically. In another embodiment, a given reactor mayremains operational and bromination and decoking occur simultaneously inthe same reactor.

In an embodiment while a given reactor is off-line, the overall processcan, nevertheless, be operated without interruption by using a reservereactor, which may be arranged in parallel with its counterpart reactor.For example, twin bromination reactors and twin coupling reactors may beutilized, with process gasses being diverted away from one, but notboth, bromination reactors (or coupling reactors) when a decokingoperation is desired. The use of a fluidized bed may reduce cokeformation and facilitate the removal of heat and catalyst regeneration.

Another embodiment of the decoking process may involve non-oxidativedecoking using an alkane or mixture of alkanes, which may reduce boththe loss of adsorbed products and the oxygen requirement of the process.

In still another embodiment of the decoking process, an oxidant such asoxygen, air, or enriched air may be co-fed into the bromination sectionto convert the coke into carbon dioxide and/or carbon monoxide duringthe bromination reaction, thus eliminating or reducing the off-linedecoking requirement. The reactor configuration may comprise a catalyticbed for the bromination of hydrocarbons followed by a metal bromide bedto capture any unreacted oxygen.

In the embodiment shown in FIG. 5, a bromination reactor capable ofbeing decoked during operation may comprise one or more catalytic zonesuseful for the bromination of a hydrocarbon with a metal halide catalystzone located near the center of the reactor. As a hydrocarbon and anelemental halide are introduced into the reactor, the halide may reactwith the hydrocarbon to form an alkyl halide and some coke on thehalogenation catalyst. The oxygen present in the feed to the reactor mayreact with any coke formed during the halogenation of the hydrocarbonsto produce oxidation products (e.g., CO, CO₂, water, etc.). In addition,the oxygen may react with a portion of the hydrocarbons or halogenatedhydrocarbons to form oxidation products. Any oxygen reaching the metalhalide catalyst zone may react with the metal halide to form a metaloxide and elemental halogen. This halogen may then further react withany unreacted hydrocarbons to form alkyl halides. The reactor may becyclically operated in a forward and reverse mode to remove coke buildupon any catalyst present in either side of the metal halide zone. Thereactor may be a fixed bed reactor, including a vertical fixed bedreactor, a radial bed reactor, or any other suitable fixed bed typereactor.

Appropriate catalyst types for the metal bromide zone may include anyactive catalyst or solid reactant useful in capturing oxygen and formingan elemental halide, as described in more detail below. The activematerials may be either redox active or non-redox active. Suitablematerials may include, but are not limited to, oxides or halides ofcopper, mangesium, yttrium, nickel, cobalt, iron, calcium, vanadium,molybdenum, chromium, manganese, zinc, lanthanum, tungsten, tin, indium,bismuth, or combinations thereof. An oxide of these metals may form ametal halide in situ upon exposure to any hydrogen halide generatedduring the halogenation reaction. In an embodiment, a non-redox activecatalyst such as NiO/NiBr₂ may be preferred due to its high brominecapacity and stability at high temperature in the reactor. In anembodiment, a NiBr₂ catalyst may be used in the center of the reactor.This bromination configuration can prevent oxygen break through whereBr₂ is generated from a metal bromide (e.g., CuBr₂) for use in thebromination reaction, including use at high pressures. The oxygenflowrate through the reactor may be less than about 5% by volume, oralternatively, less than about 3% by volume during the decoking process.Further, the decoking process may occur periodically to oxidize anybuilt-up coke deposits, or oxygen may be continuously fed to the reactorin a continuous decoking process.

Alkyl Halide Separation

The presence of large concentrations of polyhalogenated species in thefeed to the coupling reactor may result in an increase in cokeformation. In many applications, such as the production of aromatics andlight olefins, it may be desirable to feed only monohalides to thecoupling reactor to improve the conversion to products. In oneembodiment of the invention, a specific separation step may be addedbetween the halogenation/reproportionation reactor(s) and the couplingreactor.

For example, a distillation column and associated heat exchangers may beused to separate the monobromides from the polybrominated species byutilizing the large difference in boiling points of the compounds. Thepolybrominated species that are recovered as the bottoms stream may bereproportionated with alkanes to form monobromide species and olefins,either in the bromination reactor or in a separate reproportionationreactor. The distillation column may be operated at any pressure rangingfrom about 1 atm to about 50 atm. The higher pressures may allow highercondenser temperatures to be used, thereby reducing the refrigerationrequirement.

FIG. 6 illustrates one embodiment of a separation unit for separatingmonobromides from polybrominated species. Alkyl bromides from thebromination reactor may be cooled by passing through a heat exchanger70, and then provided to a distillation column 71 equipped with two heatexchangers 72 and 73. At the bottom of the column, heat exchanger 72acts as a reboiler, while at the top of the column heat exchanger 73acts as a partial condenser. This configuration allows a liquid“bottoms” enriched in polybromides (and containing no more than a minoramount of monobromides) to be withdrawn from the distillation column.The polybromides may be passed through another heat exchanger 74 toconvert them back to a gas before they are returned to the brominationreactor (or sent to a separate reproportionation reactor) forreproportionation with unbrominated alkanes. At the top of the column,partial reflux of the liquid from the reflux drum is facilitated by theheat exchanger 73, yielding a vapor enriched in lighter componentsincluding methane and HBr, and a liquid stream comprised of monobromidesand HBr (and containing no more than a minor amount of polybromides).

Alternate distillation configurations may include a side stream columnwith and without a side stream rectifier or stripper. If the feed fromthe bromination reactor contains water, the bottoms stream from thedistillation column will also contain water, and a liquid-liquid phasesplit on the bottoms stream may be used to separate water from thepolybrominated species. Due to the presence of HBr in the water stream,it may be sent to a HBr absorption column or to the bromine generationreactor.

Catalytic Coupling of Alkyl Halides to Higher Molecular Weight Products

The alkyl halides produced in the halogenation/reproportionation stepmay be reacted over a catalyst to produce higher hydrocarbons andhydrogen halide. The reactant feed may also contain hydrogen halide andunhalogenated alkanes from the bromination reactor. According to theinvention, any of a number of catalysts may be used to facilitate theformation of higher hydrocarbon products from halogenated hydrocarbons.Nonlimiting examples include non-crystalline alumino silicates(amorphous solid acids), tungsten/zirconia super acids, sulfatedzirconia, zeolites, such as SAPO-34 and its framework-substitutedanalogues (substituted with, e.g., Ni or Mn), ZSM-5 and itsion-exchanged analogs, and framework substituted ZSM-5 (substituted withTi, Fe, Ti+Fe, B, or Ga). Preferred catalysts for producingliquid-at-room-temperature hydrocarbons include ion-exchanged ZSM-5having a SiO₂/Al₂O₃ ratio below about 300, preferably below about 100,and most preferably about 30 or less. Nonlimiting examples of preferredexchanged ions include ions of Ag, Ba, Bi, Ca, Fe, Li, Mg, Sr, K, Na,Rb, Mn, Co, Ni, Cu, Ru, Pb, Pd, Pt, and Ce. These ions can be exchangedas pure salts or as mixtures of salts. The preparation of doped zeolitesand their use as carbon-carbon coupling catalysts is described in PatentPublication No. US 2005/0171393 Al, which is incorporated by referenceherein in its entirety. In another embodiment, a fluorinated aluminabased solid reactant, as described in more detail below, may be used asthe catalyst or as a support for a catalytic material useful in theformation of higher hydrocarbon products. Use of a fluorinated aluminamay allow for the simultaneous formation of higher hydrocarbons andcapture of hydrogen halide formed in the reaction.

In one embodiment of the invention a Mn-exchanged ZSM-5 zeolite having aSiO₂/Al₂O₃ ratio of 30 is used as the coupling catalyst. Under certainprocess conditions, it can produce a tailored selectivity of liquidhydrocarbon products.

In one embodiment of the invention, a reduced aluminum content ZSM-5zeolite may be used as a coupling catalyst. Generally, a dealuminationtreatment of the coupling catalyst may provide benefits such as higherselectivity towards BTX products while maintaining high conversion(>about 99%). Additionally dealumination may extended the catalystuseful life, may improve short and long term thermal stability, and mayalso reduce coke generation. Dealumination of a zeolite catalyst may bedone by selective treatment of the hydrogen-exchanged zeolite with acompound that specifically reacts with aluminum centers by formingeither volatile compounds at high temperature or soluble complexes whentreated in an aqueous solution. Examples of dealumination agents mayinclude mineral acids, such as hydrochloric acid (HCl), hydrofluoricacid (HF), ethylenediaminetetraacetic acid (EDTA), oxalic acid, malonicacid; overheated water steam (steaming), and exchange reagents (SiCl₄,NH₄[SiF₆], NH₄HF₂, AlF₃, trialkyl phosphates, organic phosphites).

Coupling of haloalkanes may be carried out in a fixed bed, fluidizedbed, or other suitable reactor, at a suitable temperature (e.g., about150° C. to about 600° C., preferably about 275° C. to about 425° C.) andpressure (e.g., about 0.1 atm to about 35 atm) and a residence time (τ)of from about 1 second to about 45 seconds. In general, a relativelylong residence time favors conversion of reactants to products, as wellas product selectivity, while a short residence time means higherthroughput and (possibly) improved economics. It is possible to directproduct selectivity by changing the catalyst, altering the reactiontemperature, and/or altering the residence time in the reactor. Forexample, at a moderate residence time of 10 seconds and a moderatetemperature of about 350° C., xylene and mesitylenes may be thepredominant components of the aromatic fraction(benzene+toluene+xylenes+mesitylenes; “BTXM”) produced when the productof a methane bromination reaction is fed into a coupling reactor packedwith a metal-ion-impregnated ZSM-5 catalyst, where the impregnationmetal is Ag, Ba, Bi, Ca, Co, Cu, Fe, La, Li, Mg, Mn, Ni, Pb, Pd, or Sr,and the ZSM-5 catalyst is Zeolyst CBV 58, 2314, 3024, 5524, or 8014,(available from Zeolyst International, Valley Forge, Pa.). At a reactiontemperature of about 425° C. and a residence time of about 40 seconds,toluene and benzene may be the predominant products of the BTXMfraction. Product selectivity may also be varied by controlling theconcentration of dibromomethane produced or fed into the couplingreactor. Removal of reaction heat and continuous decoking and catalystregeneration using a fluidized bed reactor configuration for thecoupling reactor may be anticipated in some facilities.

In an embodiment, the coupling reaction may be carried out in a pair ofcoupling reactors, arranged in parallel. This allows the overall processto be run continuously, without interruption, even if one of thecoupling reactors is taken off line for decoking or for some otherreason. Similar redundancies can be utilized in the bromination, productseparation, halogen generation, and other units used in the overallprocess.

In some embodiments, the catalytic coupling of alkyl halides to highermolecular weight products may result in the formation of olefins. Inthese embodiments, the alkyl halides produced in thehalogenation/reproportionation step may be reacted over a catalyst toproduce higher hydrocarbons and hydrogen halide. The reactant feed mayalso contain hydrogen halide and unhalogenated alkanes from thebromination reactor. In one embodiment, the coupling reactions takeplace in a single coupling vessel with a single catalyst system as shownin FIG. 7. In another embodiment two or more catalyst systems are used,each in its own reactor. FIG. 8 illustrates this for two catalystsystems, although more may be used. In another embodiment of theinvention (not illustrated), two or more catalysts may be mixed togetherusing a single reaction vessel. For convenience, the drawings illustratefixed bed reactors. In other embodiments of the invention, the reactorsystems may use fixed bed, moving bed, fluidized bed, or any othersuitable reactors or combinations of these reactors types.

According to the invention, any of a number of catalysts or acombination of two or three of these catalysts may be used to facilitatethe formation of light olefins from halogenated hydrocarbons.Nonlimiting examples include various crystallinesilico-alumino-phosphates and alumino silicates, such as SAPO-34 and itsframework-substituted analogues (substituted with, e.g., Co, Ni, Mn, Gaor Fe), ZSM-5 and its metal doped analogs (doped with Mg, Ca, Sr, Ba, K,Ag, P, La, or Zn), erionite, ferrierite, ALPO-5, MAPO-36, ZSM-12,ZSM-57, ZSM-23, ZSM-22 and MCM-22. Catalysts for producing light olefinsmay include SAPO-34, CoSAPO-34 (Co substituted SAPO-34), alkaline earthmetal doped ZSM-5 having a loading amount below about 20% in weight,preferably in the range of about 0.5% to about 10%. The synthesis andpreparation procedures for these materials are described in the Examplesherein.

Coupling of alkyl halides to olefins may be carried out in a fixed bed,moving bed, fluidized bed, or any other suitable reactor, at a suitabletemperature (e.g., about 300° C. to about 600° C., preferably about 400°C. to about 500° C.) and pressure (e.g., about 0.1 atm to about 10 atm.)and a residence time (τ) of from about 0.1 seconds to about 10 seconds.In general, a relatively short residence time may favor conversion ofreactants to desired products, as well as improving product selectivity.It may be possible to direct product selectivity by changing thecatalyst, altering the reaction temperature, and/or altering theresidence time in the reactor. For example, with a ZSM-5 based catalyst(e.g. 5% Mg/8014), at a short residence time (<1 s) and moderatetemperature (about 400° C.), propylene is the predominant component oflight olefins. With a SAPO-34, at a reaction temperature higher than450° C., ethylene is the predominant component of the light olefins.Removal of reaction heat and continuous decoking and catalystregeneration using a fluidized bed reactor configuration for thecoupling reactor may be anticipated in some embodiments of theinvention.

In other embodiments, the catalytic coupling of alkyl halides to highermolecular weight products may result in the formation of alcohols oroxygenates. In an embodiment, the resulting MeBr may be reacted over asuitable catalyst (e.g., Ca silicate as described in more detail herein)to form alcohols or other oxygenates, generating HBr and H₂O in theprocess.

In another embodiment, the formation of oxygenates may take place in asingle reaction vessel. In this embodiment an aqueous solution of SeO₂may be used to form alcohols and/or other oxygenates. The use of anaqueous SeO₂ solution is described in more detail below.

In some embodiments, the catalytic coupling of alkyl halides to highermolecular weight products may result in the formation of aromaticcompounds such as mesitylene. In one embodiment, a suitable catalyst toform mesitylene may be a modified ZSM-5 catalyst. One example of asuitable modified ZSM-5 catalyst may be a copper oxide (CuO)/zinc oxide(ZnO) modified ZSM-5 catalyst synthesized using a wet-impregnationtechnique.

One example of a suitable wet-impregnation technique may include using ametal nitrate solution to coat a catalyst support followed by calcining.For example, copper nitrate and zinc nitrate may be dissolved inde-ionized water to form a solution. If necessary, the pH value of thesolution may be adjusted by adding a base, such as ammonium hydroxide. AZSM-5 zeolite catalyst may then be added to the solution and allowed tosoak. In some embodiments, the catalyst may soak in the solution forabout 24 hours. After the catalyst has been soaked in solution, theexcess water may be removed under vacuum and the catalyst may be driedand calcined. The material may be heated to between about 100° C. andabout 150° C. for about 12 hours to remove at least some water. Thedried material may then be calcinated at about 450° C. to about 850° C.for about 6 hours using a heating rate of about 1° C./min. One exampleof a suitable modified ZSM-5 catalyst is an about 7% CuO/0.5% ZnOimpregnated ZSM-5 catalyst with a silica to aluminum ratio of about 55.

Reduction of Coke in the Catalytic Coupling Reaction

As previously noted, the process of producing higher hydrocarbons usingalkyl halides may generates coke (a carbon rich solid residue) as anundesired byproduct on the catalyst and reactor walls. Furthermore, itmay reduce productivity due to the need for de-coking on a regularbasis. In some embodiments, a Lewis base molecule, such as water, carbondioxide and carbon monoxide, may be added to the catalyst to reduce theamount of coke that is generated. It is believed that the Lewis basemolecule, such as water, reacts with the most reactive carbocations onthe surface of the catalyst preventing the elimination of hydrogen richfragments and consecutive conversion to coke. In addition, the Lewisbase molecule may react with the Lewis acidic sites on the catalyst,thereby preventing them from generating coke. In some embodiments, itmay be desirable to continuously supply Lewis base molecules as theadsorption of the Lewis base on the catalytic acidic centers isreversible at the conditions of the reaction. In an embodiment, lessthan about 15%, or alternatively less than about 10% by weight of theLewis base may be added to control the formation of coke.

Hydrocarbon Product Separation and Halogen Recovery

The coupling products may include higher hydrocarbons and HBr. In theembodiments shown in FIGS. 1 and 2, products that exit the couplingreactor may first be cooled in a heat exchanger and then sent to anabsorption column. HBr may be absorbed in water using a packed column orother contacting device. Input water and the product stream may becontacted either in a co-current or counter-current flow, with thecounter-current flow preferred for its improved efficiency. HBrabsorption may be carried out either substantially adiabatically orsubstantially isothermally. In one embodiment, the concentration ofhydrobromic acid after absorption ranges from 5 to 70 wt %, with apreferred range of 20 to 50 wt %. The operating pressure may range fromabout 1 atm to about 50 atm, more preferably from about 1 atm to about30 atm. In the laboratory, a glass column or glass-lined column withceramic or glass packing may be used. In a pilot or commercial plant,one or more durable, corrosion-resistant materials, as described in moredetail below, may be utilized.

In one embodiment of the invention, the hydrocarbon products may berecovered as a liquid from the HBr absorption column. This liquidhydrocarbon stream may be phase-separated from the aqueous HBr streamusing a liquid-liquid splitter and sent to the product cleanup unit. Inanother embodiment, the hydrocarbon products are recovered from the HBrcolumn as a gas stream, together with the unconverted methane and otherlight gases. The products may then be separated and recovered from themethane and light gases using any of a number of techniques. Nonlimitingexamples include distillation, pressure swing adsorption, and membraneseparation technologies.

In some embodiments, the product clean-up unit may comprises or includea reactor for converting halogenated hydrocarbons present in the productstream into unhalogenated hydrocarbons. For example, under certainconditions, small amounts of C₁-C₄ bromoalkanes, bromobenzene, and/orother brominated species may be formed and pass from the couplingreactor to the liquid-liquid splitter 15 and then to the productclean-up unit 17 as shown in FIG. 1. These brominated species may be“hydrodehalogenated” in a suitable reactor. In one embodiment, such areactor comprises a continuous fixed bed, catalytic converter packedwith a supported metal or metal oxide catalyst. Nonlimiting examples ofthe active component may include copper, copper oxide, palladium, andplatinum, with palladium being preferred. Nonlimiting examples ofsupport materials include active carbon, alumina, silica, and zeolites,with alumina being preferred. The reactor may be operated at a pressureof about 0 psi to about 150 psi, preferably from about 0 psi to about 5psi, and a temperature of about 250° C. to about 400° C., preferablyabout 300° C. to about 350° C., with a GHSV of about 1200 hr⁻¹ to about60 hr⁻¹, preferably about 240 hr⁻¹. When bromobenzene (e.g.) is passedover such a reactor, it is readily converted to benzene and HBr, withsome light hydrocarbons (e.g., C₃-C₇) produced as byproducts. Althoughcarbon deposition (coking) may deactivate the catalyst, the catalyst maybe regenerated by exposure to oxygen and then hydrogen at, e.g., 500° C.and 400° C., respectively.

After HBr is separated from the hydrocarbon products, the unconvertedmethane may leave with the light gases in the vapor outlet of the HBrabsorption unit. In one embodiment of the invention, unconverted methanemay be separated from the light gases in a separation unit (“SEP II” inthe FIGS.), which operates using pressure or temperature swingadsorption, membrane-based separation, cryogenic distillation(preferable for large-scale production), or some other suitableseparation process. Low methane conversions in the bromination reactormay result in the coupling products being carried with the light gases,which in turn may necessitate the recovery of these species from thelights gases. Separation technologies that may be employed for thispurpose include, but are not limited to, distillation, pressure ortemperature swing adsorption, and membrane-based technologies.

In another aspect of the invention, a process for separating anhydrousHBr from an aqueous solution of HBr is provided. HBr forms ahigh-boiling azeotrope with water; therefore, separation of HBr from theaqueous solution requires either breaking the azeotrope using anextractive agent or bypassing the azeotrope using pressure swingdistillation. FIG. 9 illustrates one embodiment of an extractivedistillation unit for separating HBr from water. Water may be extractedin a distillation column 80 and HBr may be obtained as the distillatestream 81. The distillate stream may also contain small amounts ofwater. In one embodiment, the distillation column 80 is a tray-tower ora packed column. Conventional ceramic packing may be preferred overstructured packing Aqueous bromide salt, such as CaBr₂, may be added atthe top of the distillation column, resulting in the extraction of waterfrom aqueous HBr. A condenser may not be required for the column. Areboiler 83 may be used to maintain the vapor flow in the distillationcolumn. The diluted stream of aqueous CaBr₂ 82 may be sent to theevaporation section 86, which, optionally has a trayed or packedsection. The bottoms stream from the column may be heated beforeentering the evaporation section. Stream 87 may comprise mostly water(and no more than traces of HBr) and may leave the evaporation section.

In one embodiment, HBr may be displaced as a gas from its aqueoussolution in the presence of an electrolyte that shares a common ion (Bror H⁺) or an ion (e.g. Ca²⁺ or SO₄ ²⁻) that has a higher hydrationenergy than HBr. The presence of the electrolyte pushes the equilibriumHBr_(aq)

HBr_(gas) towards gas evolution, which may be further facilitated byheating the solution.

Aqueous solutions of metal bromides such as CaBr₂, MgBr₂ also KBr, NaBr,LiBr, RbBr, CsBr, SrBr₂, BaBr₂, MnBr₂, FeBr₂, FeBr₃, CoBr₂, NiBr₂,CuBr₂, ZnBr₂, CdBr₂, AlBr₃, LaBr₃, YBr₃, and BiBr₃ may be used asextractive agents, with aqueous solutions of CaBr₂, MgBr₂, KBr, NaBr,LiBr or mixtures thereof being preferred. The bottoms stream of thedistillation column may contain a diluted solution of the extractingagent. This stream may be sent to another distillation column or avaporizer where water may be evaporated and the extracting agent may beconcentrated before sending it back to the extractive distillationcolumn. Sulfuric acid may be used as an extracting agent if its reactionwith HBr to form bromine and sulfur dioxide may be minimized.Experiments carried out to demonstrate the separation of anhydrous HBrfrom an aqueous solution of HBr are described in Examples 2 and 3.

In another aspect of the invention shown in FIG. 10, a process forseparating anhydrous HBr from an aqueous solution of HBr is providedusing temperature swing absorption. As described above, HBr may beabsorbed from the products stream using an aqueous solution. The effectof temperature on the solubility of HBr in water is shown in FIG. 11.The HBr absorption column may use aqueous HBr as the feed such that theoverall feed concentration is at least about 48% by weight HBr, andafter absorbing HBr, the outlet concentration may be between about 50%and about 80% HBr by weight. In an embodiment, the outlet of theabsorption system may be a concentrated aqueous HBr stream with aconcentration of at least about 48% HBr by weight, with a preferredconcentration between about 55% and about 75% HBr by weight. Theconcentrated aqueous HBr stream may be sent to the evaporation state forHBr recovery. In an embodiment, the absorption column may be glass linedcarbon steel or polymer lined carbon steel. Graphite heat exchangers maybe used in the process.

In an embodiment, the absorption column may be a packed column. Inanother embodiment, a tray column may be used. The absorption column mayoperate at a temperature of about 150° C. or lower. As a large amount ofheat may be generated during HBr absorption, the heat may be removedusing an external circulation heat exchanger. The hydrocarbon productsmay leave in the gas outlet.

Higher boiling hydrocarbons may condense and leave with the outlet,where they may be separated using a liquid-liquid phase separator (notdepicted in the drawing), since aqueous HBr and hydrocarbons phaseseparate. At pressures above about 5 atm, the liquid hydrocarbons may beeasily separated from light gases and HBr by cooling the stream andusing flash separation before introducing the gas into the absorptioncolumn. As a general trend, the temperature required for an HBr strippermay increase with pressure. After phase separation, aqueous HBr is sentto a heater where the temperature is increased. The decrease in HBrsolubility at this temperature results in HBr removal in the gas phase.In some embodiments, trace amount of water may be removed with the HBr.However, in most cases, measurements in the laboratory did not detectany water present in the HBr vapor. The aqueous HBr may exit theheater/evaporator and may be cooled before recirculation to theabsorption column.

In another aspect of the invention, various approaches to productclean-up (separation and/or purification) are provided. A number ofbromide species may be present in the unpurified product stream: HBr,organic bromides such as methyl bromide and dibromomethane, andbromo-aromatics. In one embodiment of the invention, hydrocarbonproducts may be separated from brominated species by passing the productstream over copper metal, NiO, CaO, ZnO, MgO, BaO, or combinationsthereof. Preferably, the products may be run over one or more of theabove-listed materials at a temperature of from about 25° C. to about600° C., more preferably, about 400° C. to about 500° C. This processmay be tolerant of any CO₂ that may be present.

In still another embodiment, HBr may be separated from the hydrocarbonproducts stream using distillation. Since HBr is the largest componentin the C—C coupling product stream and has the lowest boiling point(about −67° C. at 1 atm), the distillation process must be performed ata higher pressure. A schematic for the separation system is shown inFIG. 12. If the products from coupling are at a lower pressure, they maybe compressed to a pressure of about 10 atm or higher and the firstcolumn (Col 1) may separate methane and light gases from HBr and higherboiling components. The distillate may consist of a small amount of HBr.The distillate stream is compressed to a pressure of about 15 atm orhigher to increase the condenser temperature for the demethanizer (Col2). The bottoms stream of the demethanizer consists of ethane with asmall amount of HBr. The bottom stream from the first column (Col 1) maybe sent to a series of distillation columns (Cols. 3 and 4) where HBrmay be separated and sent to the bromine generation section (not shown),and the light gases and liquid hydrocarbon products are obtained as thedistillate and bottoms, respectively. Compression needs may be reducedif the coupling reactor is operated at a higher pressure. In certainembodiments, the coupling product inlet to the separation system may beat a high pressure of about 15 atm to about 40 atm and hence compressionmay not be needed downstream.

In another embodiment, particularly for large-scale production ofhydrocarbons, unconverted methane may be separated from other lighthydrocarbons as well as heavier products (e.g., benzene, toluene, etc.)using distillation. For example, in FIGS. 1 and 2, methane and otherlight hydrocarbons exit the absorption column through a gas outlet andare directed to a separation unit (SEP. II). Any unconverted methylbromide may be removed with the light gases and may be recycled back tothe bromination/reproportionation reactor. Heavier hydrocarbons may beremoved as a liquid distillate.

Molecular Halogen Generation

In one embodiment of the invention, catalytic halogen generation may becarried out by reacting hydrohalic acid and molecular oxygen over asuitable catalyst. The general reaction may be represented by equation(1):

The process may occur at a range of temperatures and mole ratios ofhydrohalic acid (HX) and molecular oxygen (O₂), e.g., about 4:1 to about0.001:1 HX/O₂, preferably about 4:1 (to fit the reaction stoichiometry),more preferably about 3.5:1 (to prevent eventual HBr breakthrough).

Halogen may be generated using pure oxygen, air, or oxygen-enriched gas,and the reaction may be run with a variety of inert nonreacting gasessuch as nitrogen, carbon dioxide, argon, helium, and water steam beingpresent. Any proportion of these gases may be combined as pure gases orselected mixtures thereof, to accommodate process requirements.

A number of materials have been identified as halogen generationcatalysts. It is possible to use one type of catalyst or a combinationof any number, configuration, or proportion of catalysts. Oxides,halides, and/or oxy-halides of one or more metals, such as Cu, Ag, Au,Fe, Co, Ni, Mn, Ce, V, Nb, Mo, Pd, Ta, or W are representative, morepreferably Mg, Ca, Sr, Ba, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, or Ce. Themost preferable catalysts are oxides, halides, and/or oxy-halides of Cu.These materials may be considered cataloreactants as discussed in moredetail below.

Although not bound by theory, the following equations are consideredrepresentative of the chemistry believed to take place when suchmaterials are used to catalyze halogen formation:

CaO+2HBr→CaBr₂+H₂O  (2)

CaBr₂+½O₂→CaO+Br₂  (3)

for metal oxides in which the metal does not change oxidation states,and

Co₃O₄+8HBr→>3CoBr₂+4H₂O+Br₂  (4)

3CoBr₂+2O₂→Co₃O₄+3Br₂  (5)

for metal oxides in which the metal does change oxidation states. Thenet reaction for equations (2)+(3) and equations (4)+(5) is equation(7):

which is equivalent to equation (1).

In one embodiment of the invention, chlorine is used as the halogenatingagent, and ceria (CeO₂) is used to catalyze the generation of chlorinefrom hydrochloric acid. The following equations are consideredrepresentative:

2CeO₂+8HCl→2CeCl₃+4H₂O+Cl₂  (8)

2CeCl₃+2O₂→2CeO₂+3Cl₂  (9)

for an overall reaction: 2HCl+½O₂→H₂O+Cl₂  (10)

which is also equivalent to equation (1).

This use of ceria is quite novel, as it allows essentially completeconsumption of HCl. In contrast, previous reactions of metal oxides,HCl, and oxygen have typically yielded HCl/Cl₂ mixtures. Thus, ceria canadvantageously be employed as a halogen regeneration catalyst,particularly where chlorine is used for alkane halogenation, withchlorine's attendant lower cost and familiarity to industry.

In one embodiment of the invention, the halogen generation catalyst(s)may be supported on porous or nonporous alumina, silica, zirconia,titania or mixtures thereof, or another suitable support. A range oftemperatures may be employed to maximize process efficiency, e.g., about200° C. to about 600° C., more preferably about 350° C. to about 450° C.

Solid reactant Removal of Hydrogen Halide and Halide Regeneration

In another embodiment, the hydrogen halide generated during catalyticcoupling may be separated from the product stream and regenerated usinga cataloreactant. A cataloreactant may facilitate carbon-carboncoupling, e.g., hydrocarbon oligomerization or metathesis. The term“cataloreactant” may refer to an inorganic compound that (a) contains atleast one metal atom and at least one oxygen atom, and (b) facilitatethe production of a higher hydrocarbon. Nonlimiting examples ofcataloreactants include zeolites, doped zeolites, metal oxides, mixedmetal oxides, metal oxide-impregnated zeolites, and similar materials,mixtures of such materials, as well as any other material describedherein for capturing and converting hydrogen halides. Nonlimitingexamples of dopants include alkaline-earth metals, such as calcium andmagnesium, and their oxides and/or hydroxides. A nonlimiting list ofmetal oxides may include oxides of copper, magnesium, yttrium, nickel,cobalt, iron, calcium, vanadium, molybdenum, chromium, manganese, zinc,lanthanum, tungsten, tin, indium, bismuth, and mixtures thereof.

Without wishing to be limited by theory, it is believed that acataloreactant may differ from a true catalyst as it may be converted toa metal halide when exposed to a hydrogen halide. The metal oxide maythen be regenerated by treating the metal halide with oxygen or air(preferably at an elevated temperature) to allow at least some of thecataloreactant to be recycled within the process. The cataloreactant mayalso act as a halogen release and sequestering agent, offering thepossibility of obtaining a tunable coupling product distribution. Thechoice of cataloreactant may allow the product distribution to includethe ability to produce oxygenates if desired. The overall chemical cyclemay result in water being created as the only byproduct of the reaction.When used solely for hydrogen halide capture, a cataloreactant may bereferred to as a solid reactant. Further, the use of a solid reactantfor hydrogen halide capture and elemental halide recovery reduceshalogen inventory, simplifies the process operations and may reduce theoverall capital cost.

In an embodiment, a cataloreactant may be redox or non-redox active. Asused herein, the term “non-redox active” may refer to a metal or a metaloxide that has a single, stable oxidation state. For example, anon-redox active metal or metal oxide may include, but is not limitedto, Ni, Ca, Mg, or Ba. Non-redox active metals or metal oxides maycapture and sequester a hydrogen halide without releasing an elementalhalide in the process. For example, equations (2) and (3) presentedabove demonstrate a non-redox active cataloreactant that may effectivelycapture a hydrogen halide. As used herein, the term “redox active” mayrefer to a metal or metal oxide that has more than one stable oxidationstate. For example, a redox active metal or metal oxide may include, butis not limited to, Cu, Co, Ce, or Fe. An advantage of using redox activemetal oxides is that they may be regenerated at a lower temperature,enabling a substantial decrease in the energy needed in the overallprocess. Redox active metals or metal oxides may generate elementalhalide when used in the hydrogen halide capture and regeneration cycle.For example, equations (4) and (5) presented above demonstrate aredox-active cataloreactant in the context of a bromine based systemthat may release elemental bromine during the hydrogen bromide capturereaction. The amount of element halogen released, if any, by aredox-active system may depend on the halide used, the conditions of thereactor, and the choice of cataloreactant material.

In an embodiment, a solid reactant may be used to capture and oxidizehydrogen halide. In this embodiment, a stream containing a hydrogenhalide may be passed over the solid reactant to generate thecorresponding metal halide. The solid reactant may be a redox ornon-redox active material. The hydrogen halide capture reaction may begeneralized as:

MO (metal oxide)+2HX

MX₂ (metal halide)+H₂O

for a non-redox active solid reactant.

In an embodiment, the stream containing the hydrogen halide may comefrom a variety of sources. For example, the hydrogen halide may begenerated as a result of an aqueous absorption of the hydrogen halidefrom the products stream exiting the coupling reactor. Alternatively,the stream containing the hydrogen halide may be the products streamleaving the bromination reactor or the coupling reactor. In stillanother embodiment, the stream containing the hydrogen halide may havebeen partially separated from the products stream exiting the couplingreactor. For example, any hydrogen halide may be separated from theproducts stream along with a methane stream or a light hydrocarbonstream before being passed to a vessel containing a solid reactant. Inthese embodiments, the solid reactant may be used to capture anyhydrogen halide contained within the stream, resulting in a stream thatmay be essentially free of hydrogen halide.

A solid reactant material that has been converted into a metal halidemay be regenerated by treatment with air or oxygen to release anelemental halogen and convert the solid reactant back into the originaloxide material. As used herein, the term “air or oxygen” may include anynumber of oxygen-based or oxygen-containing gas streams. Examplesinclude, without limitation, ordinary air, pure oxygen gas (O₂), oxygengas containing minor amounts of other gaseous components, dilute streamsof oxygen gas in a carrier gas (e.g., helium), oxygen-enriched air, etc.Exposure to air or oxygen may regenerate the metal halide species backinto the corresponding metal-oxygen species. Upon regeneration, theelemental halide that is release may be recycled for use in thebromination reactor or elsewhere in the process. The reaction in theregeneration section may generally be represented as:

MX₂ (metal halide)+½O₂

MO (metal oxide)+X₂

In an embodiment, the performance characteristics of the solid reactantmay be important as well as determine the reactor configuration bestsuited for a specific application. Important characteristics mayinclude, but are not limited to, a high capacity for holding regenerablebromine, the stability of the bromine capacity over thousands of cycles,and the ability to rapidly neutralize HBr and regenerate the originalsolid reactant upon contact with air or oxygen.

In an embodiment, the solid reactant materials may be formed by usingsol gel formulations, co-precipitation formulations, and wetimpregnation, as disclosed herein. In addition, a solid reactant maycomprise small amounts of enabling chemicals to enhance the stability ofthe solid and the rate of bromine regeneration. For example, potassiumoxide and yttrium-stabilized zirconium may enhance the stability andreaction rates of the solid reactants during the HBr capture and brominegeneration reactions.

The various steps of hydrogen halide capture and release may be carriedout in a vessel, container, or reactor at appropriate pressures andtemperatures. Factors that may affect the reactor conditions include,but are not limited to, the feedstock or composition of the hydrogenhalide stream, the solid reactant composition, the flow rates, and thereactor type. In an embodiment, the reactor may be operated at, orslightly above, atmospheric pressure. In another embodiment, the reactormay be operated at a pressure ranging from about 1 atmosphere to about200 atmospheres. In an embodiment, the reactor may be operated betweenabout 0° C. to about 600° C., alternatively between about 200° C. toabout 500° C. to facilitate hydrogen halide capture depending on thesolid reactant material selected. For example, NiO or CaO may be used tocapture HBr at a temperature between about 425° C. and about 500° C. fora non-redox active material based processes, while cobalt oxide orcerium oxide may be used for HBr capture at a temperature between about300° C. and about 450° C. for a redox active material based process. Inan embodiment, the reactor may be operated between about 0° C. to about650° C., alternatively between about 200° C. to about 600° C. duringhalogen oxidation and release. This may regenerate the metal halidespecies back into the corresponding metal-oxygen species. Uponregeneration, elemental halide will be released, which may be recycledfor use in the bromination reactor or elsewhere in the process. Forexample, NiBr₂ or CaBr₂ may be reacted with air or oxygen at atemperature between about 400° C. and about 600° C. to regeneratebromine in a non-redox active material based process, while cobaltbromide or cerium bromide may be reacted with air or oxygen at atemperature between about 200° C. and about 550° C. to regeneratebromine in a redox active material based process.

Materials for Hydrogen Halide Removal and Regeneration

In an embodiment of the processes described herein, various materialsmay act as a catalyst or cataloreactant active material, or a support.In some embodiments, gaseous HBr may be selectively removed from theproduct stream through the use of a calcium silicate based solidreactant. In this embodiment, as the gaseous HBr is removed from theproduct stream it may be directly converted to Br₂ in a second stepusing a suitable oxidant, for example oxygen. Generally, it is desirablethat the calcium silicate based solid reactant have a high brominecapacity, e.g. greater than 4 mmol Br₂/cm³, cyclically stable over manycycles, be in a form such that it may be used in either fixed, moving,or fluidized bed reactors, and have a minimal environmental, health andsafety risk. In one embodiment, a suitable calcium silicate based solidreactant may be synthesized using a wet-impregnation technique. Usingthe wet-impregnation technique, a metal nitrate may be used to preparethe solid reactant, however any soluble compound would be suitable. Inone embodiment, calcium nitrate and ethanol may be mixed in an amountsufficient such that the calcium nitrate dissolves. Additional metalnitrates, such as potassium nitrate, may also be added. The solute maythen be combined with a suitable silica material of appropriate particlesize. The mixture may then be refluxed at a temperature of approximately100° C. for approximately three to five hours and then allowed to dry.The dried material may then be heated to 200° C. to remove the NOxcomponent and then the materials may be calcined at approximately 550°C. for six hours at a heating rate of about one to five ° C./min.

While calcium silicate based solid reactants suitable for use in thepresent invention may be prepared in a variety of ways, calcium silicatebased solid reactants prepared using the wet-impregnation techniquedescribed herein have been tested at neutralization temperatures of 400°C. and regeneration temperatures of 500° C. for 100 cycles with noapparent loss of capacity, other than an initial break in period of 5-20cycles. Additionally, calcium silicate based solid reactants prepared bythis method may be in a useable form as synthesized (up to ˜2 mmpellets) and may require no additional binding agent for fixed bedapplications. Calcium silicate based solid reactants may provide stablebromine capacities of about 1.5 mmol Br₂/g-solid to about 3 mmolBr₂/g-solid or greater. In some embodiments, the basicity of the calciumsilicate based solid reactants may be increased via the addition ofalkali metals, which may increase regeneration rates. For example, theaddition of potassium in a molar ratio of about 5:20:75 (K:Ca:SiO₂) mayincrease reaction rates about 5 times when compared with materials withonly calcium.

In an embodiment, a nickel oxide (NiO)-based nano-composite may be usedas a solid reactant for selective capture of HBr and its subsequentconversion to Br₂. The materials used for the NiO based-nano compositemay exhibit high capacity (about 4 mmol Br₂/g or higher), fast Br₂generation rates, and long term cycle stability. As used herein, theterm “cycle stability” is defined to mean that key properties of thesolid reactant, such as, but not limited to, capacity, capture andregeneration rates, etc., do not change appreciably as the solid isrepeatedly cycled between the oxide and bromide states, as well asbetween low and high temperature. Various wet-chemical embodiments maybe used to synthesize nano-composite solid reactants, including sol-gel,sol-gel coupled with oil-drop, and co-precipitation based methods, asdescribed in more detail below. While these embodiments may be describedin terms of NiO-based solid reactants for HBr capture/Br₂ regeneration,the synthesis techniques may also be applicable for other metal oxidebased solid reactants. Non-limiting examples include cobalt, copper,calcium, and iron oxides for capture/Br₂ regeneration. In addition,these techniques may also be applicable for regenerable solid reactantsfor CO₂ removal (ZnO

ZnCO₃) and chemical looping combustion (NiO

Ni).

In another embodiment, gaseous HBr may be selectively removed from theproduct stream through the use of a fluorinated alumina based materials.A metal oxide doped fluorinated alumina (e.g., FAl₂O₃) may be a stablesolid reactant for hydrogen halide capture and elemental halogenregeneration. In some embodiments, a fluorinated alumina material, suchas a calcium oxide doped fluorinated alumina, may be used as acataloreactant for methanol synthesis. As a catalyst FAl₂O₃ may beeffective in converting some olefins (e.g., isobutylene) to higherhydrocarbons, and may be used as a catalyst or component of a catalystfor alkyl halide coupling into higher hydrocarbons. Fluorinated aluminamaterials may exhibit a stable bromine capacity of about 2.0 to about2.5 mmol Br₂/g for many cycles, for example up to about 500 cycles. Thefluorinated alumina materials may exhibit high catalytic activity due tostrong interactions between the fluorinated support crystal structureand any additional metals or metal oxides doped or ion exchanged withthe material. The presence of fluorine in the material may result inenhanced Lewis acidity which may also account for a high level ofcatalytic activity. Catalysts or cataloreactants prepared using afluorinated alumina material may be suitable for use in fixed, moving,and fluidized bed applications.

Additional materials may be used with a fluorinated alumina material toform a catalyst or cataloreactant for use in the production of higherhydrocarbons. For example, NiO and CaO may be supported on a highsurface area fluorinated alumina. These materials may be doped with oneor more alkali or alkali earth metals, which may increase the elementalhalide regeneration rates when these materials are used. While notintending to be limited by theory, it is believed that unlike an inertsupport, a fluorinated alumina material may react with an activematerial (e.g., a metal oxide such as NiO, CaO, etc.) as a consequenceof the material's Lewis acidity, which may result in surfaceimmobilization of the active material. The immobilization of the activematerial may reduce or eliminate sintering, which may lead to catalystor cataloreactant degradation.

High surface area fluorinated alumina (FAl₂O₃) may be synthesized byimpregnating a high surface area alumina with an aqueous solution ofammonium fluoride, which is used as a fluorinating agent. After stirringthe mixture for a sufficient amount of time at room temperature, theexcess solution may be evaporated. The resulting material may be driedin an oven, followed by calcination under N₂. Additional materials maythen be further added to the fluorinated alumina. For example, nickelnitrate or calcium nitrate may be used to wet impregnate the fluorinatealumina followed by calcining to produce a NiO or CaO doped fluorinatedalumina, respectively.

In an embodiment, an active material may comprise less than about 30%,or alternatively, less than about 15% by weight fluorine in an aluminastructure. The base alumina may be any suitable alumina and may include,for example, spheres, ellipsoids, toroids, etc. In an embodiment, analumina sphere about 2 to about 3 millimeters (commercially available asDavicat Al-2750 from W.R. Grace & Co. of Columbia, Md.) may be used asthe starting material for the synthesis of a fluorinated alumina.

In another embodiment, hydrogen halide generated in the processdescribed herein may be removed using a metal halide salt with aplurality of oxidation states. In an embodiment, the metal may becopper, which may form two stable oxidation states with a halide such asbromine. In an embodiment in which the halogen is bromine, copper mayform both CuBr and CuBr₂. By cycling between the two oxidation states ofCu, a closed recycle loop of bromine may be created wherein bromine ismostly retained as a bromide salt.

In an embodiment, brominated alkyls from the bromination reactor may becoupled by contact with an appropriate catalyst to yield products andHBr. Gases from the coupling reactor may be cooled and contacted withwater to absorb HBr and allow the mostly HBr-free coupling products tobe sent to product separation and recovery. The aqueous solution of HBrmay be contacted with CuBr, which may be recycled from a brominegeneration step described below. Air or oxygen may be utilized tofacilitate a reaction between HBr and CuBr resulting in the conversionof the CuBr to CuBr₂ and water. In another embodiment, an aqueoussolution of CuBr/CuBr₂ may be used as the absorbent in the contactseparation of the coupling reactor products from the HBr.

The CuBr₂, unreacted CuBr solids, and water may be separated using anytechnique capable of removing solids from an aqueous solution. Forexample, suitable separation techniques may include, but are not limitedto, crystallization or evaporative crystallization followed byfiltration or centrifugation. The CuBr₂ crystals, which may stillcontain water, may be dried at a temperature low enough to avoid brominerelease. In an embodiment, the drying temperature may be below about200° C. The dried CuBr₂ crystals may then be sent to a brominegeneration unit.

In an embodiment, the bromine generation unit may comprise a heatingchamber for heating the CuBr₂ to about 275° C., resulting in theconversion of the CuBr₂ to CuBr and the release of bromine as a vapor.In this embodiment, a carrier gas may be used to remove the brominegenerated by the CuBr₂ in the bromine generation unit. In an embodiment,the carrier gas may be methane or any other light hydrocarbon stream.The bromine generation unit products, including bromine and any lighthydrocarbons making up the carrier gas, may be separated from the solidCuBr and sent to a bromination reactor where the bromination reactionmay be carried out. The bromine generation unit products may be heatedin order to raise the temperature of the mixture to the temperaturedesired in a bromination reactor. The solid CuBr that is generated maybe recycled to the HBr capture reactor. In some embodiments, the brominegeneration reactor and the bromination reactor may take place in thesame vessel.

In another embodiment, the copper bromide based process described abovemay be used as a scavenging material to capture any hydrogen halidepassing to a process stream exiting the process. For example, an aqueoussolution or a dry bed of CuBr may be used as a final HBr trap prior toany vent streams leaving the process. Such traps may prevent any HBrfrom escaping the process and allow the HBr to be subsequently capturedand converted to elemental bromine for reuse in the process.

Methods of Preparing Catalysts and Cataloreactants

Any of the materials useful as coupling catalysts, or even brominationor oxidation catalysts, may be synthesized using a variety of methods.As mentioned above, a NiO based nano-composite (e.g., powder form) solidreactant may be synthesized using a sol-gel based procedure. One exampleof a typical sol-gel based procedure for the synthesis of nano-compositesolid reactant (powder form) is described in FIG. 13. For example, tosynthesize a NiO-K₂O—Y₂O₃—ZrO₂—Al₂O₃ nano-composite, an aluminumprecursor (e.g., aluminum isopropoxide or aluminum tri-sec-butoxide) andzirconium propoxide may be dissolved in isopropanol. The overallconcentration of Al(III) may be about 0.6 M (generally controlled in therange of about 0.1 to about 1.0 M). Deionized water may then be addeddrop-wise. Hydrolysis may occur upon adding the water and may bepromoted by stirring at about 60° C. (generally at about 40 to about 90°C.) to produce a sol solution. A nickel precursor (e.g., nickel nitrateor chloride), potassium nitrate and yttrium nitrate, all of which are atleast partially water soluble, may be dissolved in deionized water witha concentration of about 3.0 M (generally about 1 to about 6 M). TheNi/K/Y solution may be added and the resulting sol solution may then bestirred for approximately 30 minutes with heating when the total volumeof the sol solution is reduced by about 30 to about 50% by evaporation.The sol gel may be peptized at 60° C. by adding 1 M nitric acid (theamount of the acid may be determined by the molar ratio of protons toAl(III) of about 0.05 to about 0.4), which may result in the formationof a gel. To ensure good mixing of all the cations, the gel mixture maythen be further stirred for several hours. The gel may be dried in anoven at about 110° C. to about 150° C., where the exact temperature maydepend on the amount of nickel precursor used. The dried material may becalcined at about 450° C. to about 850° C. for about 6 hours using aheating rate of about 1° C./min. The resulting material may have anominal composition of about 51% NiO-2% K₂O-0.6% Y₂O₃.4.4% ZrO₂-42%AlO₃.

Another method for synthesizing nano-composite solid reactants mayutilize sol-gel techniques coupled with oil-drop (e.g., pellet form).One example of this method is described in FIG. 14. For example, inorder to synthesize a NiO—AlO₃ nano-composite pellet, nickel nitrate ofan appropriate amount may be added and mixed with an aqueous sol ofboehmite at 75° C. for about 2 hours. Nitric acid may then be added topeptize the sol solution, with pH controlled in the range of about 0 toabout 5. A wet gel may be obtained after heating and stirring at about50° C. for another hour. An organic acid such as acrylic acid may alsobe added to the gel as a polymerization initiator. The wet gel may bedropped into an immiscible paraffin oil layer and spherical shapedgranules may form. The granules may pass through the oil layer and fallinto an ammonia solution containing a predetermined concentration ofnickel nitrate, where they may be aged from about 1 hour to about 5days. During the aging process, the wet gel granules may become rigidgel particles (e.g., pellets). The solid granules may then be removedand washed with water and ethanol, which may be followed by drying atabout 100° C. to about 150° C. Calcination may be conducted at about450° C. to about 850° C. for about 6 hours with a heating rate of about1° C./min.

FIG. 15 illustrates a co-precipitation method, which is yet anotherexample of a method for synthesizing nano-composite solid reactants. Forexample, in order to synthesize a NiO—AlO₃ nano-composite solidreactant, an aqueous solution of nickel nitrate and aluminum nitrate maybe stirred at about 45° C. while an about 5.8% NH₃.H₂O solution may beadded drop-wise. The hydroxides of nickel and aluminum may start toprecipitate and the final pH may be controlled in the range of about 8to about 11. The whole solution may then be aged at about 45° C. forabout one day before it is filtered. The precipitates may be washed withdeionized water and dried at about 100° C. to about 150° C. The driedpowder may then be calcined at about 450° C. to about 750° C. for about6 hours with a heating rate of about 1° C./min.

Examples of other suitable nano-composite solid reactants may includeabout 30% NiO—Al₂O₃ by sol-gel; about 30% NiO—Al₂O₃ with K doping bysol-gel; about 50% NiO—Al₂O₃ with K and YSZ doping by sol-gel; and about42% NiO—La₂O₃—Al₂O₃ by co-precipitation.

All the above synthesis methods may yield a nano-composite materialcomprising a metal oxide (e.g., NiO) and one or more additionalcomponents (e.g., AlO₃, K, YSZ, or La₂O₃). The main variables in thesynthesis procedure may be the different components in the composite andtheir respective compositions, pH, aging time/temperature, concentrationof the metal oxide in the ammonia aging solution, and calcinationtemperature.

The composition of the metal oxide in the nano-composite has been foundto have an important impact on both the capacity of the material as wellas its stability. If the composition of the metal oxide is too low, thenthe material will have a small, but stable capacity (e.g., NiOcomposition at about 30% results in a stable capacity of about 1 mmolBr₂/g, which may be too small for commercial applications). However, ifthe composition of the metal oxide is too high, the material may exhibita high initial capacity, which may start to decrease rapidly withrepeated oxide/bromide cycles. (e.g., an about 70% NiO—AlO₃nano-composite material prepared using a sol-gel synthesis procedure mayshow an initial capacity of about 7.0 mmol Br₂/g, which may thendecrease to about 2 mmol Br₂/g after less than about 250 cycles).

While the exact mechanism by which these nano-composite materialsexhibit their desired properties (e.g., cycle stability, fast reactionrates, etc.) as a solid reactant is not known, it is believed that theyare due to a combination of the structure of the nano-composite materialitself as well as the nature and compositions of the other componentswithin the nano-composite. The near molecular level dispersion of theactive metal oxide within the nano-composite material may result inthermodynamic properties that do not favor particle sintering as thematerial cycles between the oxide and bromide states. In addition, it isalso believed that surface reactions between the metal oxide and atleast some of the other components may immobilize the metal oxide,thereby preventing, or significantly reducing, loss of surface area dueto sintering. For example, NiO—La₂O₃—AlO₃ and NiO—AlO₃ nano-compositesexhibit stable capacities of about 4.0 mmol Br₂/g and about 3.0 mmolBr₂/g, respectively, while a NiO—SiO₂ nano-composite may lose capacityquickly as it cycles (e.g., the material has an initial capacity ofabout 3.0 mmol Br₂/g, but drops to about 1.5 mmol Br₂/g after about 180cycles it). These trends may hold true even if all three materials aresynthesized using a similar techniques and conditions.

In addition to impacting the cycle stability of the materials, the othercomponents in the composite may also affect the rate of Br₂ generation.For example, adding alkaline metals (e.g., Li, Na, K and Cs) maysignificantly increase the Br₂ regeneration rates of NiOnano-composites. Also oxygen-ion conducting compounds have also beenfound to be effective in enhancing the Br₂ generation rates of thesematerials. For example, it is believed that Y₂O₃—ZrO₂ in the compositemay react in part to form yttria-stabilized-zirconia, YSZ, which may bean oxygen conducting compound.

In some embodiments, the nano-composite solid reactants may beencapsulated. It may be desirable to encapsulate a nano-composite tostabilize the particle size and surface area. In one embodiment,encapsulation may be achieved by water-in-oil microemulsion, organictemplate directing solution evaporation, or Stober-like methods. Factorsto be considered when encapsulating a solid reactant includeporosity/pore size and void space inside the shell.

Aqueous Process for Hydrogen Halide Removal and Halide Regeneration

In an embodiment, hydrogen halide may be oxidized to generate acorresponding elemental halide using an aqueous solution with anappropriate catalyst. The catalyst may take advantage of the change inthe oxidation state of a material with multiple oxidation states. Invarious embodiments, the aqueous based process may be described inconnection with HBr and Br₂ and the semi-metals Se and Te, but it shouldbe apparent to one skilled in the art that the process is not limited tothe described embodiments. Both selenium and tellurium are semi-metalsthat have several oxidation states including −2, 2, 4 and 6. Additionalelements with multiple oxidation states include, without limitation,Cu(II)/Cu(I), Fe(III)/Fe(II), Sb(V)/Sb(III), Mn(IV)/Mn(II), V(V)/V(IV),As(V)/As(III), and Ru(IV)/Ru(III). The following description usesselenium as example although the same description applies to telluriumand the other elements with multiple oxidation states unless notedotherwise.

The aqueous based oxidation process takes advantage of the reductioncapability of Se (I) and Se(II) compounds towards oxygen from the air,which may be oxidized to Se(IV). The Se(IV) state is a sufficientlystrong oxidizer and may be capable of oxidizing HBr/Br⁻ to elementalbromine. In such a cycle the selenium may shuttle between the twooxidation states and converts the HBr to Br₂ using air or oxygen atrelatively mild conditions.

The cycle starts with Se(IV) compound such as SeO₂, which may be in anacidic environment (an acidic environment may enhance the oxidationpower of Se(IV)). A first series of reactions (Eq. 11 to Eq. 17) has thenet effect of converting HBr into Br₂ and H₂O and converting Se(IV) toSe(II).

SeO₂+4HBr→SeBr₄+2H₂O  (Eq. 11)

SeBr₄→SeBr₂+Br₂  (Eq. 12)

2SeBr₄→Se₂Br₂+Br₂  (Eq. 13)

Se₂Br₂→SeBr₂+Se  (Eq. 14)

2Se₂Br₂+2H₂O→SeO₂+4HBr+3Se  (Eq. 15)

Se+O₂→SeO₂  (Eq. 16)

3SeBr₂→Se₂Br₂+SeBr₄  (Eq. 17)

SeBr₄ is an orange red crystalline solid that may dissociate attemperatures exceeding 70° C. yielding Se, Se₂Br₂, SeBr₂, and Br₂.Heating HBr and SeO₂ in a closed vessel above 45° C. may lead tosublimation of SeBr₄ crystals. Similarly, heating in an open containeror in the presence of inert pass through gas may result in free Br₂being liberated along with the other products-metallic selenium, whichmay appear as a solid powder precipitate upon cooling, and the lowerbromides Se₂Br₂ and SeBr₂ observed as refluxing red oily liquid (Se₂Br₂is dark red, pungent oily liquid which boils at about 225° C. to about230° C.).

The reaction according to Eq. 11 may take place at approximately roomtemperature or lower while the remainder of the equations may take placeat a temperature ranging from about 65° C. to about 300° C. and apressure ranging from about 0.1 atm to about 40 atm. At the temperatureof the reaction the bromine may be evaporated from the reactor alongwith water vapor due to the reactions shown in Eq. 12 through Eq. 14.Despite the existence of an HBr-water azeotrope, HBr may not escape thesystem because practically all of the bromine may be bound as seleniumspecies and the solution may contain relatively low HBr concentrationsat or below the azeotropic composition. However, the process may betolerant to the presence of small amounts of HBr in the vapor phase.

A second series of reactions (eq. 18-eq. 20) may result in theregeneration of the active Se(IV). This may be done eithersimultaneously or sequentially with the first set of reactions:

2Se(II)+O₂+4H⁺→2Se(IV)+2H₂O  (Eq. 18)

Se(IV) may not oxidize Br₂ to BrO₃ ⁻. The electrode potential for theBr₂ to BrO₃ ⁻ reaction is about 1.482 V which is above the oxidationpotential of Se(IV)/Se(II). The electrode potential for Br₂/BrO⁻ isabout 1.574 V, which may be high enough so that the reaction tohypobromite does not occur. The selenium redox potentials are not ashigh, making any such oxidation unlikely to occur. Even if generated insmall amounts BrO⁻ and BrO₃ ⁻ may not leave the system due to thefollowing reactions in the acidic environment in the reactor:

5Br⁻+6H⁺BrO₃ ⁻→3Br₂+3H₂O  (Eq. 19)

Br⁻+BrO⁻+2H⁺→Br₂+H₂O  (Eq. 20)

These reactions may maintain a low concentration of any seleniumoxybromides as they may react as soon as they are formed. The two mainproducts leaving the system may include bromine and water. Under normaloperating conditions, these components may leave as vapor. The othercomponents of the reaction mixture may generally be nonvolatile.However, trace components other than bromine and water may appear in theproducts stream depending on the conditions and type of the reactor.

A benefit of this process is the safety of operation. Although some ofthe reactants may be volatile and toxic compounds (e.g., SeBr₄ andSe₂Br₂), the hazard may be reduced or eliminated by using a large amountof water in the event of a spill. Water may rapidly change the toxic,volatile bromides to inert solids (Se) and non-volatile aqueous species(e.g., SeO₂). For example, equations 11 and 12 demonstrate the reactionsof SeBr₄ and Se₂Br₂ with water.

SeBr₄+2H₂O→SeO₂+4HBr  (Eq. 21)

2Se₂Br₂+2H₂O→Se+SeO₂+4HBr  (Eq. 22)

In an embodiment using iodine and selenium, or iodine and tellurium, thesame set of equations may apply (e.g., Eq. 11-Eq. 22), and thus,selenium or tellurium may be used as a catalyst for the oxidation ofhydrogen iodide to iodine. In this embodiment, the pressure may rangefrom about 0.1 atm to about 40 atm, while the operating temperature maybe lower as HI is a stronger reducing agent. For example, thetemperature of the system may range from about 0° C. to about 120° C. Insome embodiments, tellurium and selenium may be used to converthydrochloric acid to chlorine, though higher temperatures may berequired. For example, the temperature may range from about 150° C. toabout 500° C., which may result in the reactions occurring in the gasphase. Such reactions may generally be described by equations 11 through14. Tellurium may be used as a catalyst for the bromine generation fromhydrogen bromide with chemical processes identical to those describedfor the selenium system above; however the temperatures may be higherthan for selenium. In an embodiment that utilizes tellurium to generatebromine from hydrogen bromide, the reaction temperature may range fromabout 100° C. to about 350° C.

FIG. 16 illustrates a schematic embodiment of a reactor system for theconversion of HBr to Br₂. In this embodiment, a stream containing HBr 90and a stream containing air or oxygen 91 may be fed to a reactor 92containing an aqueous solution of selenium bromide, various oxybromides(e.g., SeOBr₂, Se₂Br₂ etc.), or any combination thereof. Selenium oxide,if present during the reaction, may be in a slurry phase. Products maybe removed from the reactor as a vapor stream. The reactor outlet stream93 may contain selenium bromide and HBr. Due to the presence of theHBr-water azeotrope and the fact that the boiling point of seleniumbromide is higher than either bromine or water, it may be possible touse a reactive distillation system 94 to fractionate the reactor outlet93 whereby only bromine, water, unconverted oxygen, and nitrogen leavethe system in the product mixture 95. The bottoms stream 96 may returnany selenium compounds to the reactor 92. In an embodiment, theperformance of the system may be improved by changing the feed stage andnumber of stages of the fractionator 94. In another embodiment, theperformance of the system may be improved by adding an additionalreboiler, by varying the reflux and reboil ratios, or a combinationthereof. The product mixture 95 containing bromine, water, oxygen andnitrogen may be processed using any of the methods disclosed herein.

In another embodiment, any hydrogen halide generated in the couplingreactor may be separated from the coupling products, any unreactedfeedstock, and any other inert gases by passing the entire couplingreactor product stream through the aqueous Se catalyst system. In thisembodiment, the coupling reactor products stream may be cooled prior toentering the aqueous Se catalyst system to prevent overheating andboiling of the aqueous reaction medium. The HBr may be adsorbed by theaqueous phase and phase separate from any hydrocarbons, including anyproducts and unreacted feedstock. The aqueous Se system enriched in HBrmay then be re-circulated back to the bromine generation reactor whereit may be converted to bromine. This approach may eliminate the need fora separate HBr/coupling products reactor, thus reducing the overallcapital costs. In this embodiment, the aqueous Se system may be oxidizedto convert the Se species to highly water soluble H₂SeBr₆ and H₂SeO₃before being contacted with the coupling reactor product stream. Suchoxidation may help prevent transferring any of the Se compounds into theorganic phase and contaminating the final product stream.

The reactor depicted in FIG. 16 may a CSTR (continuous stirred tankreactor), however other conventional reactors such as CSTRs in series,PFR (plug flow reactor), packed columns, reactors with multiple inletsand vapor outlets, multiple reactors in series, and other reactor typesknown to those skilled in the art may also be used.

In another embodiment, the MeBr created in the bromination reaction maybe reacted directly in the aqueous oxidation process to Br₂. This wouldrequire operation at mildly acidic conditions. An advantage would be thesimplicity of the process.

The process may require three reaction stages characterized by thefollowing equations:

CH₄(g)+Br₂(g)=>CH₃Br(g)+HBr(g)  (eq. 23)

CH₃Br(aq)+H₂O(aq)=>CH₃OH(aq)+HBr(aq)  (eq. 24)

2HBr(aq)+½O₂(aq)=>H₂O(aq)+Br₂(aq) (Using SeO₂ catalyst)  (eq. 25)

First, methane may be brominated (eq. 23). The resulting bromomethanemay be fed to a reactor containing water, and hydrolysis to producemethanol may take place (eq. 24). Hydrogen bromide may be produced inboth Eq. 23 and Eq. 24. Hydrogen bromide may be oxidized in an aqueoussolution by the action of oxygen in the presence of catalytic seleniumdioxide (eq. 15)

Thermal bromination of methane proceeds according to (eq. 13).Conversion of methyl bromide to methanol and aqueous HBr (eq. 14) isbased on the well known reactivity of alkyl halides towards hydrolysis.In general this reaction may be fast for alkyl bromides at temperaturesat about 100° C. and pressures at about 1 to about 10 atm. Eq. 15 may beachieved at about 100° C. through the use of SeO₂ as a catalyst.

Recovery and Recycle of Molecular Halogen

Halogen generation produces both water and molecular halogen. Water maybe separated from halogen and removed before the halogen is reacted withthe hydrocarbon feedstock. Where the halogen is bromine, abromine-water, liquid-liquid phase split may be achieved uponcondensation of a mixture of these species. For example, in anembodiment, a liquid-liquid flash unit may be used to separate most ofthe bromine from water, simply and inexpensively. The bromine phasetypically contains a very small amount of water, and may be sentdirectly to the bromination reactor. The water phase, however, maycontain 1-3 wt % bromine. However, if air is used in the brominegeneration step, nitrogen and unconverted oxygen may be present with thebromine and water stream that enters the flash.

The gas leaving the flash unit primarily consists of nitrogen andunconverted oxygen, but carries with it some bromine and water. Theamount of bromine leaving with the vapor phase may depend on thetemperature and pressure of the separation unit. The flash may beoperated at temperatures ranging from about 0° C. to about 50° C.;however, a lower temperature (e.g., about 2° C. to about 10° C.) ispreferred to reduce bromine leaving in the vapor stream. In anembodiment, the operating pressure is about 1 bar to about 50 bar, morepreferably about 1 bar to about 30 bar. In an embodiment, the vaporstream may be sent to the bromine scavenging section for brominerecovery, as described below.

Bromine contained in the water-rich phase leaving the liquid-liquidflash may be effectively recovered by distillation. The presentlydescribed distillation subprocess may produce bromine or bromine-waterazeotrope as a distillate, which may be recycled back to the flash unitor to a hydrogen halide oxidation process, as disclosed herein. Thebottoms stream may consist mainly of water. Bromine may react reversiblywith water to form small amounts of HBr and HOBr. In the distillationscheme, therefore, ppm levels of HBr (and/or HOBr) may be present in thebottoms stream. A side-stream rectifier or stripper may be utilized toreduce the bromine content of the bottoms stream to produce a pure waterstream. Other alternatives that may reduce the bromine content of thewater to below 10 ppm range include, but are not limited to, theaddition of acids such as sulfuric acid, hydrochloric acid, andphosphoric acid, in very small quantities to reduce the pH of the waterstream. Lowering the pH may drive the HBr and HOBr stream back tobromine and water, thereby substantially reducing the loss of bromine inthe water stream. HBr present in the water stream may also be recoveredusing ion-exchange resins or electrochemical means.

Recovery of All Halogen for Reuse

Various streams in the process may contain some halogen that may berecovered prior to venting or otherwise allowing the stream to exit theprocess. Such streams may result from separation of the bromine fromlighter components such as nitrogen or oxygen. For example,condensation, vapor-liquid separation, gas-solid adsorption/reaction, orany combination thereof may be used to separate residual bromine in avapor stream from the other components of the stream. The vent streamsmay be treated in order to recover the halogen prior to venting theother components of the stream. In an embodiment, any scavenging methodmay be used that is capable of recovering at least some elementalhalogen or hydrogen halide from a process stream. For example, a chilledliquid process or a solid scavenging process may be used to recover anyhalogen.

In an embodiment, the scavenging process may consist of a single passtechnique, or a variety of techniques may be used in series. In someembodiments, a general scavenging technique such as a chilled brineprocess may be used to remove the majority of the halogen in a streamprior to treating the stream with a high capture efficiency scavengingtechnique such as solid adsorption/reaction. Such an embodiment mayallow a high capture efficiency while avoiding an excessive burden onthe final bromine adsorption/reaction, which may be the most expensiveportion of the scavenging process. To achieve low levels of residualbromine the temperature of the stream being treated may need to bereduced to about 10° C. to about −30° C. The process stream being cooledmay contain a variety of components such as water and bromine, which mayfreeze under these conditions. Therefore, simple cooling by indirectheat transfer may not suffice due to icing of the heat transfer surface.Such a problem may be overcome by introducing a brine coolant which maydirectly contact the process stream containing the halogen. Due the lowfreezing point associated with brines, the use of a brine may enablecooling to the desired temperature. Vaporizing the bromine by heatingthe brine can then occur, with further heating employed to facilitateconcentration (e.g., evaporative concentration) of the brine for re-use.This approach to bromine recovery may be carried out either continuouslyor in batch mode.

In an embodiment, the brine solution may be composed of any salt orcombination of salts that is at least partially soluble in an aqueoussolution. In an embodiment, suitable salts may include commonlyavailable salts such as NaCl or CaCl₂, or any salt of a halidecorresponding to the halogen being recovered from the process stream.For example, if bromine is being recovered from a process stream, NaBror CaBr₂ may be used to form the brine solution. As used herein, theterm brine refers to an aqueous salt solution at, below, or abovesaturation. This may include salts that are undersaturated orsuper-saturated, depending on the process conditions. In an embodiment,the brine may have from about 0.1% to about 60% by weight salt in anaqueous solution. In another embodiment, the brine may have from about10% to about 30% by weight salt in an aqueous solution. The aqueoussolution may include any fluid containing water and may be derived fromany source. For example, a water stream generated in the process may beused to form at least a portion of the brine solution.

In an embodiment, the brine solution may be directly contacted with thestream containing the halogen to be recovered. The brine coolant andliquid halogen formed by direct contact cooling may be separated fromany other light gases present in the process stream in avapor-liquid-liquid separator. Liquid from the separator may consist oftwo phases, a brine phase and the a liquid halogen phase. The liquidhalogen phase may join a previously condensed halogen in the process ormay be recycled in the process for further purification. The brine phasemay be cooled and returned to the direct contact cooling operation.

In another embodiment, if the halogen captured in the direct contactcooler is dissolved in the brine and does not phase separate, thenrecovery of this halogen may be effected by heating the brine tovaporized the halogen in the brine. The vaporized halogen may becombined with vapor from a halogen generation operation, re-circulatedto an upstream process, or any combination thereof.

In an embodiment, the chilled brine process may be operated using abrine with a temperature between about 0° C. and about −30° C. duringthe direct contact operation. In another embodiment, the chilled brineprocess may be operated using a brine with a temperature between about−5° C. and about −15° C. during the direct contact operation. Anypressure between about 1 atm to about 50 atm may be used, with apressure between about 2 atm and about 30 atm being used in someembodiments.

In another embodiment, a solid halogen scavenging process may be used,either alone or in combination with a chilled liquid process. Brominescavenging may be carried out in a bed containing solid CuBr or MnBr₂,either loaded on a support or used in powder form, to capture Br₂ from agas stream that may also contain H₂O, CO₂, O₂, methane &/or N₂. In oneembodiment of the invention, bromine scavenging is performed within arange of temperatures, e.g., from about −10° C. to about 200° C. Whenbromine scavenging is complete, molecular bromine may be released fromthe bed by raising the temperature of the bed to about 220° C. orhigher, preferably above about 275° C. It is important that there belittle if any O₂ in the bed during bromine release, as O₂ will oxidizethe metal and, over time, reduce the bromine-scavenging capacity of thebed.

Hydrocarbon Product Separation

The processes of the present invention may produce a hydrocarbon productstream that may comprise water. For example, if a cataloreactant processis used to capture and regenerate HBr with the entire product streampassing through the cataloreactant, then water may be produced and passalong with the product stream. Alternatively, in a aqueous basedhydrogen halide capture process, the product stream leaving the contacttower may contain water vapor that may be removed prior to passing theproduct hydrocarbons out of the process for sale. Once any water presentin the product stream is removed, a product recovery system may be usedto further separate and recycle the hydrocarbon product stream prior tothe hydrocarbons leaving the system.

In the product recovery system shown in FIG. 17, a product stream 110leaving a hydrogen halide removal process (e.g., an aqueous absorptionprocess, a solid reactant based capture process, etc.) may besubstantially hydrogen halide free. The product stream 110 may be cooledusing a heat exchanger 112 and partially condensed in a vessel 114 toyield a vapor phase and two immiscible liquid phases. The two liquidphases may be further separated to yield an aqueous phase stream 116,which may be primarily water with a small amount of dissolvedhydrocarbons, and an organic phase stream 118 consisting of higherhydrocarbons.

The aqueous phase stream may exit the process or be utilized for variousprocesses within the system. For example, the water may be used as awater source for another process within the system, such as a watersource or makeup water source for an aqueous hydrogen halide absorptionprocess. In another embodiment shown in FIG. 18, some of the water 116recovered in the product recovery section 108 may be mixed with thecoupling product stream in a quench column 142 and recycled to thehydrogen halide capture sub-process (e.g., a solid reactant HBr capturesub-process). In an embodiment, the quench column 142 may be a packedbed, spray tower, or equivalent unit operation. The amount of waterrecycled may be chosen such that the temperature of the mixed couplingproduct stream as well as the product gas stream leaving the hydrogenhalide capture sub-process, may be above their respective dew points toinsure that little to no liquid condensation occurs in the hydrogenhalide capture sub-process. This embodiment may improve the economics ofthe entire process by reducing the cooling load in the hydrogen halidecapture sub-process and transferring it to the product recovery system.This may result in a process with a lower capital cost as the materialsof construction used for the heat transfer surfaces in the solidreactant sub-process may be significantly more expensive than those usedin the product recovery system due to the presence of a hydrohalic acid.Further, the mixing may reduce the range of the temperature cycling inthe hydrogen halide capture sub-process, which may be useful if a solidbased reactant process is used in the hydrogen halide capturesub-process.

Referring to FIG. 17, the vapor stream 120 may be primarily composed oflight gases such as N₂, methane, and other light hydrocarbons (e.g., C₂,C₃, C₄), and may be saturated with higher hydrocarbons (e.g., C₅ ⁺) andwater. For embodiments using relatively large gas flowrates in theprocess, the vapor stream 120 may contain a significant fraction of thetotal liquid hydrocarbon product (e.g., C₅ ⁺). In some embodiments, thevapor stream 120 may then flow to an absorber 122 where a solvent may beused to absorb at least some of the higher hydrocarbons (e.g., C₅ ⁺).The solvent may be either a pure non-volatile hydrocarbon (e.g., C₁₂H2₆,mesitylene (C₉H₁₂), etc.) or a mixture of non-volatile hydrocarbons(e.g., diesel, a mixture of high boiling coupling products, etc.). Inaddition to absorbing at least some of the C₅ and higher hydrocarbons,the solvent may also absorb some of the C₃ and C₄ hydrocarbons, alongwith small amounts of the light hydrocarbons and gases. The gas stream124 leaving the absorber 122 may contain most of the N₂, CH₄, C₂, andpotential some C₃ and C₄. Stream 124 may be recycled if the amount ofnitrogen is not excessive, or it may be flared, vented, recycled to thesolid reactant sub process as a diluent for purposes of mitigating thetemperature rise in the reactors, or otherwise used within the system,for example as a fuel stream. The liquid stream from the absorber 126may pass to a separation sub-system 128, which may comprise one or moredistillation sequences for recovering (a) the solvent for recycle to theabsorber, (b) any C₃ and C₄ which may be further refined to LPG orrecycled to lights bromination; and (c) any liquid hydrocarbon products(e.g., C₅ ⁺). While this separation process may be feasible at both lowand high pressure, high pressure may be preferred in order to minimizingthe solvent flowrate and use cooling water, rather than refrigeration,in any distillation columns condensers.

An embodiment of a product recovery system with a distillation sequenceis shown in FIG. 19. In this embodiment, two distillation columns may beused to sequentially recover the light hydrocarbons, the heavyhydrocarbons, and the solvent. In the first column 130 at least some ofthe light hydrocarbons comprising C₃ and C₄ may be separated as a vaporstream 132. The heavier hydrocarbons, which may have some C₃ and C₄dissolved therein, may be passed to a second distillation column 136.The second distillation column 136 in this embodiment may separate anyremaining product hydrocarbons as a liquid stream 138 and the solvent asa liquid stream 140. The liquid stream comprising the products 138 maybe combined with the organic phase stream 118 from the initialseparation vessel 114 in the product separation sub-process. The solventstream 140 from the second distillation column 136 may be recycled backto the absorber 122. Distillation columns 130 and 136 may use a total orpartial condenser such that the light hydrocarbon stream 132 and theproduct hydrocarbon stream 138 and may be either a vapor or liquiddepending on the operating conditions. The operating pressures for thetwo distillation columns are selected so as to minimize the reboilertemperatures, minimize the use of any refrigerants in the columncondensers, and maximize the opportunity for energy integration withother sub processes in the system. Using this process and diesel as asolvent, may result in a recovery of about 100% of the C₅+ hydrocarbons,about 50% of C₄, and about 17% of C₃. The resulting overall carbonefficiency may be up to about 60%.

Still another embodiment is shown in FIG. 20. In this embodiment,feedback expansion cooling may be used to obtain a high recovery of thelight hydrocarbons. As used herein, the term “high recovery of the lighthydrocarbons” may refer to a separation process capable of recoveringmore than about 60% of the C₄, and more than about 25% of the C₃ in theinlet stream. In this process, the stream 124 may first pass through adehydration bed (not shown), and then leaving the absorber 122 may be athigh pressure. In an embodiment, stream 124 may be at a pressure greaterthan about 10 atm, or alternatively greater than about 20 atm. Thisstream 124 may be cooled using a cold process stream in a heat exchanger144 and phase separated in a separation vessel 146 to yield a liquidstream 157 comprising C₃ and C₄, along with some C₂ and C₁ and a vaporstream 148 containing N₂, CH₄ and C₂ hydrocarbons. The pressure of vaporstream 148 may be reduced from the high pressure to a much lowerpressure using an expansion turbine 150, resulting in a significantdecrease in the temperature of the stream. In an embodiment, thepressure of stream 148 may be reduced to between about 1 atm to about 5atm in the expansion turbine 150. The resulting cold gas stream 152 maybe used to cool the absorber exit gas stream 124 in the heat exchanger144. The low pressure stream 154 may then be vented, recycled if thenitrogen content is not excessive, recycled to the solid reactant subprocess as a diluent for purposes of mitigating the temperature rise inthe reactors, or otherwise used within the process, for example as afuel stream. The cold liquid stream 157 may also be used to provide someof the cooling required to cool the absorber exit stream 124 in heatexchanger 144. In another embodiment, especially in the case where theamount of the nitrogen in the absorber exit stream in not excessive, theexpansion turbine 150 may be replaced by a Joule-Thompson valve. In yetanother embodiment, the order of the expansion turbine, or theJoule-Thompson valve, and the separation vessel 146 may be reversed. Thefeedback cooling mechanism may allow the absorber gas outlet stream 124to be cooled to a temperature low enough to condense at least some C₃and C₂, without the use of refrigeration. Using this process, it may bepossible to increase the overall recovery of any C₄ hydrocarbons toabout 99%, any C₃ to greater than about 95%, and any C₂ to greater thanabout 30%. The resulting overall carbon efficiency may be up to about75%.

Another embodiment of the product recovery sub-process is shown in FIG.21. In this embodiment, feedback expansion cooling may be used toachieve the products separation without a solvent based absorptionsub-process. The high pressure gas stream 156 leaving the flash drum 114may first pass through a dehydration bed (not shown), and then may becooled using a heat exchanger 158 and a flash drum 162 to recover asubstantial portion of the C₃+ hydrocarbons in the liquid phase. In thisembodiment, a network of heat exchangers and flash drums may be used tosequentially cool and separate the hydrocarbons. The plurality of heatexchangers and flash drums may be used to prevent heavy hydrocarbonsfrom crystallizing in heat exchangers. The required cooling for thisprocess may be provided by expansion cooling of the gas stream 166leaving the heat exchanger/flash network, and optionally the heating andvaporization of the cold liquid stream 164. In the case where the amountof the nitrogen in the absorber exit stream 156 in not excessive, theexpansion turbine 168 may be replaced by one or a series ofJoule-Thompson valves. In addition, the order of some of the flash drumsand the expansion turbine (or Joule Thompson valve) may be reversed. Theresulting liquid stream 164 from the feedback expansion cooling processmay be distilled in one or more columns to yield a liquid stream 174comprising a hydrocarbon product (e.g., C₅ ⁺) and a vapor stream 176comprising the LPG stream (e.g., C₃ and C₄).

In an embodiment, the product separation process may utilize some heatintegration with other sub-processes in the system. For example, theseparation process may not require any external heat as all of theenergy required in the process may be provided by other process streams.One source of potential heat may be solid reactant sub-process if it isused to remove the hydrogen halide from the product stream.

Construction of Critical Process Elements with UniqueCorrosion-Resistant Materials

Corrosion induced by any halogen-containing process, whether in thecondensed phase or the vapor phase, presents a significant challenge inthe selection of durable materials for the construction of reactors,piping, and ancillary equipment. Ceramics, such as alumina, zirconia,and silicon carbides, offer exceptional corrosion resistance to mostconditions encountered in the process described herein. However,ceramics suffer from a number of disadvantages, including lack ofstructural strength under tensile strain, difficulty in completelycontaining gas phase reactions (due to diffusion or mass transport alongjointing surfaces), and possibly undesirable thermal transportcharacteristics inherent to most ceramic materials. Constructingdurable, gas-tight, and corrosion resistant process control equipment(i.e. shell and tube type heat-exchangers, valves, pumps, etc.), foroperation at elevated temperatures and pressures, and over extendedperiods of time, may likely require the use of formable metals such asAu, Co, Cr, Fe, Nb, Ni, Pt, Ta, Ti, and/or Zr, or alloys of these basemetals containing elements such as Al, B, C, Co, Cr, Cu, Fe, H, Ha, La,Mn, Mo, N, Nb, Ni, 0, P, Pd, S, Si, Sn, Ta, Ti, V, W, Y, and/or Zr.

According to one embodiment of the invention, the process andsubprocesses described herein may be carried out in reactors, piping,and ancillary equipment that are both strong enough and sufficientlycorrosion-resistant to allow long-term continued operation. Selection ofappropriate materials of construction depends strongly on thetemperature and environment of exposure for each process controlcomponent.

Suitable materials for components exposed to cyclic conditions (e.g.oxidizing and reducing), as compared to single conditions (oxidizing orreducing), may differ greatly. Nonlimiting examples of materialsidentified as suitable for exposure to cyclic conditions, operating inthe temperature range of from about 150° C. to about 550° C., include Auand alloys of Ti and Ni, with the most suitable being AlN alloyed Ti(more specifically Ti Grd-5) and Ni—Cr—Mo alloys with high Cr, low Fe,and low C content (more specifically ALLCOR®, Alloy 59, C-22, 625, andHX). Nonlimiting examples of materials identified as suitable forexposure to either acid halide to air, or molecular halogen to aircyclic conditions, in the temperature range about 150° C. to about 550°C., either acid halide to air, or molecular halogen to air includealloys of Fe and Ni, with the most suitable being alloys of theNi—Cr—Mo, and Ni—Mo families. Nonlimiting examples of materialsidentified as suitable for single environment conditions, in thetemperature range of from about 100° C. to about 550° C., include Ta,Au, and alloys of Fe, Co, and Ni. For lower temperature conditions(<about 280° C.), suitable polymer linings can be utilized such as PTFE,FEP, and more suitably PVDF. All materials may be used independently orin conjunction with a support material such as coating, cladding, orchemical/physical deposition on a suitable low-cost material such aslow-alloy steels.

Additional Process Configurations

FIG. 22 schematically illustrates an alternate mode of operation for acontinuous process for converting methane, natural gas, or other alkanefeedstocks into higher hydrocarbons. Alkanes may be brominated in thebromination section in the presence of water formed during brominegeneration, including recycled water. The bromination products may passeither through a reproportionation reactor or through thereproportionation section of the bromination reactor, where the lightgases may be reproportionated to form olefins and alkyl bromides byusing the polybromides as brominating agents. The reproportionationproducts, which include olefins, alkyl monobromides, some polybromides,and HBr, along with any unreacted alkanes, may then be sent to thecoupling reactor. The coupling products may be sent to avapor-liquid-liquid flash. Higher hydrocarbon products may be removed asan organic phase from the vapor-liquid-liquid flash, while aqueous HBrmay be removed as the heavier phase. The gas stream from the flash maybe sent to a separation system to recover methane and light gases, whichmay be recycled back to the bromination and reproportionation sections,respectively.

Nitrogen must be removed from the gas recycle stream if air is used asan oxidant in bromine generation. The aqueous HBr stream coming out ofthe vapor-liquid-liquid flash may be sent to the HBr/water separationsystem, where water may be recovered. The separation may be carried outin a distillation column, where pure water may be taken out as adistillate and the bottoms stream may be an aqueous solution of HBr(having a higher concentration of HBr than the feed to the distillationcolumn). The aqueous HBr stream may be sent back to the brominegeneration section, where bromine may be generated from aqueous HBr inthe presence of air or oxygen.

Alternatively, extractive distillation may be used to separate HBr fromwater. The separated HBr may be sent to the bromine generation reactorand bromine may be generated from aqueous HBr in the presence of air oroxygen. Complete conversion of HBr is not necessary in the brominegeneration reactor. Periodic decoking may be carried out for thebromination, reproportionation, and/or coupling reactors, with thebromine-containing decoking product stream being routed to the brominegeneration reactor.

Another continuous process alternative is shown in FIG. 23. Alkanes maybe brominated in the bromination section in the presence of water formedduring bromine generation, including recycled water. The brominationproducts (which include monobromides and polybromides) may pass througheither a reproportionation reactor or the reproportionation section ofthe bromination reactor, where the light gases may be reproportionatedto form alkyl bromides, using the polybromides as brominating agents.The reproportionation products—alkyl monobromides, olefins, a smallamount of polybromides, and HBr—and any unreacted alkanes may then besent to a separation unit where aqueous HBr may be separated from thealkyl bromides. Monobromides in the alkyl bromide stream may beseparated from the polybromides. The polybromides may be recycled to thereproportionation section where polybromides may react with the recyclegases to form olefins and monobromides.

The aqueous HBr separation from the alkyl bromides may be carried out ina distillation column coupled with a liquid-liquid flash. The alkylbromide stream may contain HBr. The monobromides may be fed into thecoupling section, and the products may be sent to a water absorptioncolumn where HBr produced in the coupling reactor is removed from theproducts and unconverted gas. The liquid outlet of the absorption columnmay be fed to a vapor-liquid-liquid flash separation unit, where higherhydrocarbon products may be removed as an organic phase and aqueous HBrmay be removed as the heavier phase. The gas outlet from the absorptioncolumn may be sent to a separation system to separate methane from thelight gases. The recovered methane may be recycled back to thebromination section, while the light gases may be recycled to thereproportionation section.

Nitrogen may be separated before the gases are recycled if air is usedas an oxidant in bromine generation. The aqueous HBr stream from thevapor-liquid-liquid flash may be combined with the aqueous HBr streamfrom the alkyl bromide separation section and sent to the HBr/Waterseparation system. The separation may be carried out in a distillationcolumn, where pure water may be taken out as a distillate and thebottoms stream may be an aqueous solution of HBr having a higherconcentration of HBr compared with the feed to the distillation column.The aqueous HBr stream may be sent back to the bromine generationsection, where bromine may be generated from aqueous HBr in the presenceof air, oxygen or enriched air.

Alternatively, extractive distillation may be used to separate HBr fromwater. The separated HBr may be sent to the bromine generation reactor,where bromine may be generated from aqueous HBr in the presence of air,oxygen, or enriched air. Complete conversion of HBr to bromine is notrequired during bromine generation. Periodic decoking of thebromination, reproportionation and coupling reactors may be carried out,with the bromine-containing decoking product stream being routed to thebromine generation reactor.

Another continuous process configuration is shown in FIG. 3. In thisembodiment a non-redox active solid reactant may be used to capture andregenerate the hydrogen halide generated in the halogenation reactor andthe coupling reactor. In this embodiment, an alkane feedstock stream 41may be brominated in a bromination reactor 43. The bromination products44 may be separated in a separator 45 to allow the monobrominated stream47 to pass to the coupling reactor 48, while the polybrominated stream46 may be recycled to a reproportionation reactor (not shown) or areproportionation section of the bromination reactor 43. If a separationand reproportionation scheme is used, the light gases may bereproportionated to form olefins and alkyl bromides through the use ofthe polybrominated species as brominating agents. The reproportionatedproducts, which may include olefins, alkyl monobromides, somepolybromides, and HBr, along with any unreacted alkanes, may then besent to the coupling reactor 48. The coupling reactor products 49 maythen be sent to an HBr capture reactor 55 that contains a solidreactant. The solid reactant may capture the HBr by forming a metalbromide corresponding to the metal-oxide solid reactant. The productstream 50 from the HBr capture reactor 55 may be substantially free ofHBr and may pass to a products separation unit 51. The product stream 50may be dehydrated to remove any water 54, such as any water producedduring the reaction of the HBr with the solid reactant. The productstream 50 may be further separated to allow methane 53 or other lighthydrocarbons to be separated from a heavier products stream 52 and berecycled to the inlet of the process or used as fuel.

The halogen capture process shown in the embodiment depicted in FIG. 3may generate a metal bromide 56. The metal bromide 56 may be regeneratedto the original metal oxide solid reactant in a regeneration reactor 57through the introduction of air or oxygen 58. The air or oxygen 58 mayreact with the metal bromide 56 entering the regeneration reactor 57 togenerate a regeneration products stream 59 containing elemental brominealong with any inert gases contained in the air or oxygen containingstream 58. The regeneration product stream 59 may be separated in aseparator 60 in order to remove and any inert gases 61 from the process,such as nitrogen if air is used as the oxygen source. The separator 60may also result in an elemental bromine stream 62 that may be passedback to the bromination reactor 43 in order to brominate the incomingalkane feedstock 41, recycled hydrocarbons, or any combination thereof.The regenerated metal oxide solid reactant may be transported back tothe HBr capture reactor 55 through recycle line 63. The metal bromideconversion to metal oxide and regeneration cycle in the embodiment shownin FIG. 3 may be carried out in any type of reactor capable ofcontaining a solid reactant material. Reactor configurations that may beused include, but are not limited to, fixed beds, fluidized beds, andmoving beds.

In another embodiment, the solid reactant may be contained in three ormore alternating fixed bed reactors in parallel (not shown). At anygiven time, one of the reactors is on-line for hydrogen halidecapture/neutralization; one of the reactors is on-line for elementalhalide regeneration; while the remaining reactors are offline for purge,and cooling/heating of the fixed bed reactors to the desired capture andregeneration temperatures. In this manner the overall process can beoperated continuously without interruption.

In an embodiment illustrated in FIG. 3, the coupling reactor 48, whichmay contain a coupling catalyst, may be carried out in any type ofreactor. Reactor configurations that may be used to create higherhydrocarbons include, but are not limited to, fixed beds, fluidizedbeds, and moving beds. In an embodiment, the coupling reactor 48 may becontained in a plurality of alternating fixed bed reactors (not shown).While a given reactor is off-line for decoking, the overall process can,nevertheless, be operated without interruption by using a reservereactor, which is arranged in parallel with its counterpart reactor. Forexample, twin coupling reactors may be utilized, with process gassesbeing diverted away from one, but not both, reactors.

In an embodiment illustrated in FIG. 3, the coupling reactor 48 may be amoving bed reactor or a fluidized bed reactor. In this embodiment, thecoupling reactor 48 may receive a regenerated coupling catalyst 64 andcontact the regenerated coupling catalyst 64 with a brominatedhydrocarbon stream 47. Coke may be produced during the coupling reactionresulting in decreased reactivity of the coupling catalyst. In order torestore the catalytic reactivity of the coupling catalyst, a decokingprocess may be carried out in a decoking reactor 65 that may receive thecoked catalyst stream 68 and air or oxygen 66 to facilitate the removalof the coke from the coupling catalyst. The decoking products stream 67,which may contain bromine, may be routed to the bromine generationreactor 57. The regenerated coupling catalyst 64 may be transported backto the coupling reactor 48 to complete the cycle.

Still another continuous process configuration is shown in FIG. 24. Inthis embodiment, a single reactor may be used to couple the alkylbromide reactants and capture the HBr generated during the brominationreaction and the coupling reaction. In this embodiment, the catalystused may act as both a coupling catalyst and solid reactant forcapturing HBr, which may be a non-redox active solid reactant. Forexample, a alumino silicate zeolite catalyst with wet-impregnated metaloxide may be used. In another embodiment, separate materials may beused. For example, a zeolite without a metal oxide may be used to act asa catalyst for coupling and a separate metal oxide doped zeolite may beused to capture HBr. This embodiment may allow the separate materials toincorporated into the reactor as a uniform mixture of the materials, orallow for layering of the materials to form zones within the reactor. Inan embodiment in which the reactor is a fluidized bed or moving bedreactor and separate materials are used to couple the alkyl bromides andcapture the produced HBr, the particles may be similarly sized to avoidseparation of the material into distinct phases during transport or use.The catalyst may regenerated in the regeneration section by oxidation ofcoke, and the solid reactant may be regenerate to release bromine in thereaction of the metal bromide with air or oxygen.

In the embodiment shown in FIG. 24, an alkane feedstock stream 301 maybe brominated in a bromination reactor 303. The bromination products 304may be separated in a separator 305 to allow the monobrominated stream307 to pass to the coupling reactor 309, while the polybrominated stream306 may be recycled to a reproportionation reactor (not shown) or areproportionation section of the bromination reactor 303. If aseparation and reproportionation scheme is used, the light gases may bereproportionated to form olefins and alkyl bromides through the use ofthe polybrominated species as brominating agents. The reproportionatedproducts, which may include olefins, alkyl monobromides, somepolybromides, and HBr, along with any unreacted alkanes, may then besent to the coupling reactor 362 that may also contain a solid reactantfor capturing HBr.

In the embodiment shown in FIG. 24, the coupling reactor may alsocontain a solid reactant for capturing any HBr in the incomingbrominated stream and any HBr produced during the coupling reaction. Theproduct stream from the coupling reactor 362 may be substantially freeof HBr and may pass to a products separation unit 315. The products maybe dehydrated to remove any water 330 contained in the system, such asthe water produced during the reaction of the HBr with the solidreactant. The products 314 may be further separated to allow methane 320or light hydrocarbons to be recycled to the inlet of the process or usedas fuel.

In an embodiment in which the coupling reactor also contains a solidreactant for capturing HBr, the coupling reaction may deactivate thecoupling catalyst and convert the solid reactant to a metal bromidephase solid reactant. The coupling catalyst may be deactivated due to anumber of reasons including, but not limited to, coke formation on thecatalyst or within the interstitial space between the catalystparticles.

In order to regenerate the coupling catalyst and the solid reactant, thematerial may be regenerated in a regeneration reactor 360 through theintroduction of air or oxygen 324. The air or oxygen may react with anycoke to generate CO₂ along with a number of other combustion productsincluding brominated species, and the metal bromide solid reactant mayreact to form a metal oxide and elemental bromine. The product stream358 from the regeneration reactor may be separated in a separator 327 inorder to remove and any inert gases 333 from the process, such asnitrogen if air is used as the oxygen source. The CO₂ generated in theregeneration reactor may be removed in separator 327 or may pass throughthe process to be removed in the products separation reactor 315. Theseparator 327 may also result in an elemental bromine stream that may bepassed back to the bromination reactor 303 in order to brominate theincoming alkane feedstock, recycled hydrocarbons, or any combinationthereof.

In the embodiment shown in FIG. 24, the coupling reaction, HBr capturereaction, and regeneration reaction cycle may be carried out in any typeof reactor capable of containing a solid coupling catalyst and solidreactant material. Reactor configurations that may be used include, butare not limited to, fixed beds, fluidized beds, and moving beds.

In another embodiment, the solid reactant may be contained in three ormore alternating fixed bed reactors in parallel (not shown). At anygiven time, one of the reactors is on-line for hydrogen halidecapture/neutralization; one of the reactors is on-line for elementalhalide regeneration; while the remaining reactors are offline for purge,and cooling/heating of the fixed bed reactors to the desired capture andregeneration temperatures. In this manner the overall process can beoperated continuously without interruption.

In an embodiment illustrated in FIG. 24, a moving bed reactorconfiguration or a fluidized bed reactor configuration may be utilizedwhere the solid reactant is cyclically transported from the couplingreactor 362 to the regeneration reactor 360 and back. In thisembodiment, the coupling reactor 362 may receive a regenerated materialstream 361 comprising a regenerated coupling catalyst, solid reactant,or combination thereof and contact the regenerated material with abrominated hydrocarbon stream 307. The coupling catalyst may bedeactivated in the coupling reactor and the solid reactant may beconverted to a metal bromide in a reaction with any HBr present. Thedeactivated coupling catalyst and the metal bromide solid reactant mayexit the reactor as a deactivated catalyst stream 359, which may betransported to a regeneration reactor 323 to be regenerated and decokedwith an air or oxygen stream 324. After regeneration, a regeneratedcatalyst stream 361 may be transported back to the coupling reactor 350to complete the cycle.

In an embodiment shown in FIG. 25, a redox active solid reactantmaterial may be used in a process for making higher hydrocarbons. Inthis embodiment, natural gas or another hydrocarbon feedstock andmolecular bromine may be carried by separate lines 401, 402 into aheated bromination reactor 403 and allowed to react. Products (e.g.,HBr, alkyl bromides, olefins, etc.), and possibly unreactedhydrocarbons, may exit the reactor and may be carried by a line 404 intoa first separation unit 405, where monobrominated hydrocarbons and HBrmay be separated from polybrominated hydrocarbons. The products may passthrough a heat exchanger 450 between the bromination reactor 403 and thefirst separation unit 405 depending on the product stream temperaturedesired in the first separation unit 405. The polybromides may becarried by a line 406 back to the bromination reactor, where they mayundergo “reproportionation” with methane and/or other lighthydrocarbons, which may be present in the natural gas and/or introducedto the bromination reactor as described below. For large scaleproduction of higher hydrocarbons, additional separation units may beemployed, which may further purify the feed stream to the couplingreactor by separating and recycling the polybromides, thereby reducingthe amount of coke and the overall bromine requirement.

In reference to FIG. 25, unreacted hydrocarbon feedstock, HBr,monobromides, and (optionally) olefins formed in the bromination reactor403 may be carried by a line 407, through a heat exchanger 408, andenter a heated coupling reactor 409, where at least some of themonobromides (and, optionally, any olefins present) may react in thepresence of a coupling catalyst to form higher hydrocarbons. Thecoupling reactor products stream comprising HBr, higher hydrocarbons,and (possibly) unreacted hydrocarbons and alkyl bromides may exit thecoupling reactor and be carried by a line 410, through an optionalcompressor 452, if required, and enter a products separation train. Anynumber or type of separation units, which may employ pressure- ortemperature-swing adsorption, membrane-based separation, cryogenicdistillation that may be preferable for large scale production, oranother suitable separation technology, may be used to generate adesired product distribution. Unreacted methane may be separated in afirst products separation unit 454 to allow the methane to be recycledto the inlet of the process or used for fuel. A second productsseparation unit 456 may be employed to separate other light hydrocarbonsand HBr from the products stream. One or more additional productseparation units as described above may be used to yield finalhydrocarbon products.

In reference to FIG. 25, the coupling reactor 409 may have a fixed bed,circulating moving bed, or circulating fluidized bed reactorconfiguration. In an embodiment, a fixed bed configuration (not shown inFIG. 25) may be used to perform the coupling reaction. In thisembodiment, a plurality of reactors may be used with the brominatedproduct stream 411 being diverted from one reactor while the other mayreceive air or oxygen to decoke the coupling catalyst. The process flowsmay then be cycled so that the coupling process may be operatedcontinuously.

In an embodiment shown in FIG. 25, the coupling reactor 409 may beoperated using a moving bed reactor configuration or a fluidized bedreactor configuration. In this embodiment, the coupling catalyst may becyclically transported between the coupling reactor 409 and a decokingreactor 412. In this embodiment, coupling reactor 409 may receive aregenerated coupling catalyst 413 and contact the regenerated couplingcatalyst with the brominated products stream 411 to form a couplingreactor products stream 410. The coupling catalyst may form at leastsome coke during the coupling reaction. The coked coupling catalyst mayexit the coupling reactor and be transported to the decoking reactor 412where air or oxygen 414 may be introduced to decoke at least a portionof the coupling catalyst. A stripping gas stream 416 (e.g., steam,hydrocarbons, etc.) may be introduced into the coked coupling catalystas it is transported between the coupling reactor 409 and the decokingreactor 412 to remove any hydrocarbons from the coked coupling catalystprior to the coked coupling catalyst being contacted with a streamcontaining air or oxygen 414. Gas stripping may be done by a discretepiece of hardware, or it may be part of the pneumatic transport systembetween zones. The decoking reaction may produce carbon dioxide as anycoke and remaining hydrocarbons adsorbed on the coupling catalystcombusts (i.e., oxidizes). These combustion products may pass out of thedecoking reactor 412 along with any inert components of the air oroxygen stream, such as nitrogen if air is used, in a decoking productsstream 415. The decoking products stream may be sent to the regenerationreactor 464 or another scrubbing section in order to recover any bromineadsorbed on the coked coupling catalyst. The regenerated couplingcatalyst 413 may be transported back to the coupling reactor 409 tocomplete the cycle. A coupling catalyst vessel 417 may be used to holdthe decoked coupling catalyst from the decoking reactor 412 before beingtransported to the coupling reactor 409. A heat exchanger 418 may beused to heat or cool the coupling catalyst to a desired temperature atwhich the coupling reaction may occur.

As shown in FIG. 25, the HBr and light hydrocarbons may be carried byline 419 into an HBr capture reactor 458 after the HBr and the lighthydrocarbons are separated from the hydrocarbon products in the productsseparation train. The conditions of the HBr capture reactor containing aredox active solid reactant may result in a metal bromide beinggenerated along with bromine, which may react with the light gases toproduce alkyl bromides. Using cobalt oxide, a redox active solidreactant, as an example, the following overall reaction occurs duringHBr capture:

Co₃O₄+8HBr→3CoBr₂+Br₂+4H₂O  (Equation 26)

C₂H₆+Br₂→C₂H₅Br+HBr  (Equation 27)

C₃H₈+Br₂→C₃H₇Br+HBr  (Equation 28)

Alkyl bromides from the HBr capture reactor 458 may pass through a heatexchanger 461, if necessary, before being separated from water byliquid-liquid or liquid-liquid-vapor phase separation 460 and sent to alights bromination reactor 462, which may also receive additionalbromine from line 468. Heat exchanger 463 may be a heater or cooler, asnecessary, to bring the stream from the separator 460 to the appropriatetemperature for the lights bromination reactor 462. The products of thelights bromination reactor 462 may be combined with the products of thebromination reactor 403 before entering the coupling reactor 409.

As shown in FIG. 25, the metal bromide produced in the HBr capturereactor 458 may be regenerated with air or oxygen to regenerate theoriginal solid reactant materials. In an embodiment, the metal bromidemay be sent to the bromine regeneration reactor 464, where the followingoverall reaction occurs:

3CoBr₂+2O₂→Co₃O₄+3Br₂  (Equation 29)

The products stream 474 from the regeneration reactor may containbromine and any inert gases contained in the air or oxygen stream 472,such as nitrogen. The products stream 474 may pass through a heatexchanger 476 to cool the stream prior to entering a separator 478. Inan embodiment, the bromine may be separated from any other componentsusing liquid-vapor separation, for example, using a flash tank. As thebromine may have a boiling point well below that of other components ofthe stream, the bromine may condense and form a liquid phase. The liquidphase may be drawn off and passed through a heat exchanger 484 beforebeing routed to the lights bromination reactor 462, the brominationreactor 403, or both. In another embodiment, the liquid bromine may bepassed to the reactor and vaporized within the reactor vessels. Thevapor stream leaving the liquid vapor separator 478 may pass through abromine scavenging unit 480 prior to exiting the system. Any brominerecovered in the bromine scavenging unit may be recycled to the system,such as for example passing through line 482 to be combined with theliquid bromine stream for use in the bromination reactors.

A fixed bed, circulating moving bed, or circulating fluidized bedreactor configuration may be used for HBr capture and bromineregeneration. In an embodiment, a fixed bed configuration (not shown inFIG. 25) may be used to perform HBr capture and regeneration. In thisembodiment, a plurality of reactors may be used with the streamcontaining the light hydrocarbons and HBr from the products separationtrain being diverted from one reactor while the other may receive air oroxygen to regenerate the solid reactant. The process flows may then becycled so that the process may be operated continuously.

In an embodiment shown in FIG. 25, a moving bed reactor configuration ora fluidized bed reactor configuration may be utilized where the solidreactant is physically cycled between the HBr capture reactor 458 andthe regeneration reactor 464. In this embodiment, an HBr capture reactor458 may receive a regenerated solid reactant 468 and contact theregenerated solid reactant with the stream containing the lighthydrocarbons and HBr 419 from the products separation train. Theregenerated solid reactant 468 may be converted to a metal bromide inthe HBr capture reactor 458 and may produce water as a byproduct. Anyhydrocarbons entering the HBr capture reactor 458 may react with anybromine generated by a redox active solid reactant. The solid reactantthat is converted in the HBr capture reactor 458 may exit the HBrcapture reactor as a metal bromide stream 470. The metal bromide stream470 may be transported to a regeneration reactor 464 where air or oxygen472 may be introduced to regenerate at least a portion of the metalbromide to the original solid reactant. A stripping gas stream 485 maybe introduced into the metal bromide as it is transported between theHBr capture reactor 458 and the regeneration reactor 464 to remove anylights or brominated lights from the metal bromide prior to the metalbromide being contacted with a stream containing air or oxygen 472. Theregenerated solid reactant stream 468 may be transported back to the HBrcapture reactor 458 to complete the cycle. A solid reactant vessel maybe used to hold the regenerated solid reactant 468 from the regenerationreactor 464 before being transported to the HBr capture reactor. A heatexchanger 471 may be used to heat or cool the regenerated solid reactantto a desired temperature at which the HBr capture reaction may occur.

In the embodiment shown in FIG. 25, a process gas stream may be usedpneumatically transport a catalyst or solid reactant stream if a movingbed or fluidized bed reactor design is used. For example, the processgas stream may be a portion of the hydrocarbon stream used as the inputinto the process. In another embodiment, an inert gas such as nitrogenmay be used to transport the catalyst or solid reactant. After thematerial is transported to the desired location, the process gas streammay be recycled within the process, used as a feed to the process, usedas a fuel stream, vented, or any combination thereof.

As shown in FIG. 26, the HBr to Br₂ conversion process using copperbromides may be applied to a process for the conversion of alkanes tohigher liquid hydrocarbons. In an embodiment, natural gas or anotherhydrocarbon feedstock may be carried by line 501 into a heated brominegeneration reactor 503. Solid CuBr₂ may be carried by line 502 into thebromine generation reactor 503 where it may be heated to about 275° C.or higher to release elemental bromine, resulting in the conversion ofthe CuBr₂ to CuBr. The bromine generation reactor products may include avapor stream 504 comprising the entering hydrocarbon feedstock and theelemental bromine and a solids stream 506 comprising CuBr and anyunconverted CuBr₂. The solids stream may pass to a HBr capture reactor,as discussed in more detail below. In an embodiment, the brominegeneration reactor 503 may be, without limitation, a moving bed reactoror a fluidized bed reactor.

The vapor stream 504 may pass to a bromination reactor 508 where thehydrocarbon feedstock may be allowed to react with the elemental bromineto form various bromination products including, but are not limited to,HBr, alkyl bromides, olefins, and possibly unreacted hydrocarbons. In anembodiment, a reproportionation scheme may be used with the brominationreactor as described in more detail herein. In this embodiment, Thebromination products may exit the reactor and be enter a separation unitwhere monobrominated hydrocarbons and HBr may be separated frompolybrominated hydrocarbons. In some embodiments, the polybromides maybe carried back to the bromination reactor, where they may undergoreproportionation with methane, other light hydrocarbons, or acombination thereof, which may be present in the natural gas and/orintroduced to the bromination reactor. In another embodiment, a separatereactor may be utilized for bromination of any C₂ or heavierhydrocarbons. In some embodiments, the bromine generation reactor andthe bromination reactor may take place in the same vessel, which may beoperated as a moving bed or fluidized bed reactor.

In the embodiment shown in FIG. 26, any unreacted hydrocarbon feedstock,HBr, monobromides, and any olefins formed in the bromination reactor maybe carried by a line 510 to coupling reactor 512, where themonobromides, olefins, or any combination thereof may react in thepresence of a coupling catalyst to form higher hydrocarbons. In anembodiment, a heat exchanger may be used to adjust the temperature ofthe brominated products stream 510 to a desired inlet temperature to thecoupling reactor 512. The coupling reactor products may include HBr,higher hydrocarbons, unreacted hydrocarbons, alkyl bromides, or anycombination thereof. The coupling reactor products may exit the couplingreactor 512 and be carried by a line 514 to an HBr separation unit 516.The coupling reactor products may pass through another heat exchanger asnecessary to adjust the temperature of the coupling products stream to adesired inlet temperature to the HBr separation unit 516.

HBr may be separated from the hydrocarbons using any suitable separationtechniques. In an embodiment, the HBr may be separated from the HBrcoupling reactor products using aqueous absorption. In this embodiment,the HBr coupling reactor products may be contacted with an aqueoussolution to absorb any HBr in the vapor stream. The resultingsubstantially HBr-free products stream may pass by line 518 to aproducts recovery unit, numerous embodiments of which are disclosedherein. In general, any light hydrocarbons contained in the productstream may be separated and directed through line 522. Any recoveredmethane may be returned to the bromination reactor and other lighthydrocarbons may be returned to a lights bromination reactor if present.Alternately, the light gases may be added to the downstream zone of thebromination reactor where they may reproportionate with polybromides toform the corresponding alkyl bromides. In still another embodiment, thelight hydrocarbons may be directed to a fuel line for use in generatingany desired energy for the process. A final products stream may bedirected through line 524 to pass out of the process.

The aqueous HBr stream leaving the absorber may be carried by a line 526to an HBr capture reactor. Air or oxygen may be fed into the unitthrough line 532 and a solid CuBr stream may be fed into the unitthrough line 506 from the bromine generation reactor 503. HBr may becaptured through the reaction of HBr and oxygen with the CuBr to yieldCuBr₂ and water. Any inert gases contained in the feed streams, such asN₂ if air is used as the oxygen source, may exit the reactor throughvent line 530. The vent line may pass through a scrubbing unit to removeany trace HBr prior to being released from the process. In anotherembodiment, an aqueous solution of CuBr/CuBr₂ may be utilized as theabsorbent in the absorption step. Alternatively, a slurry consisting ofCuBr and CuBr₂ crystals in solution saturated with respect to CuBr andCuBr₂ may be used as the absorbent.

The resulting slurry generated in the HBr Capture Reactor 530 maycontain CuBr₂, any unreacted CuBr, water, and potentially trace amountsof HBr. The slurry may be subjected to evaporative crystallization orother suitable technique to remove excess water formed in the reactionand to form additional CuBr₂ crystals. Separation of CuBr₂ crystals fromthe slurry may be accomplished by filtration, centrifugation, or anyother suitable solids/liquids separation technique. The evaporated watermay pass through line 538 to be used as a contact absorbent in theabsorber 516, to pass out of the system, or any combination thereof.

The slurry containing the solid phase crystals may pass through line 546to a dewatering unit to further remove any excess water from the solidphase CuBr and CuBr₂ crystals. The dewater unit may be any type ofprocess capable of removing additional water from the CuBr and CuBr₂crystals. For example, the dewatering unit may be a filtration unit, acentrifugal separator, or a heating unit capable of thermally drivingoff the water. The aqueous stream leaving the dewatering unit 544 may besaturated with respect to both CuBr and CuBr₂ and may contain smallamounts of solid crystals suspended in the fluid. The aqueous stream 542may pass back to the crystallizer 536 through line 542. Alternativelythe aqueous stream 542 may go to the absorber/stripper 516 and serve asthe HBr absorbent.

The CuBr₂ and CuBr crystals, which may still contain water, may be driedin a drying unit 550 at a temperature low enough to avoid brominerelease. In an embodiment, the drying temperature may be below about200° C. Any remaining water in the CuBr and CuBr₂ crystals may be drivenoff and leave the system through line 552. The water vapor may passthrough a scavenging unit to capture any bromine generated duringdrying. The dried CuBr₂ crystals may then be sent to a brominegeneration unit through line 502.

As shown in FIG. 27, an aqueous HBr to Br₂ conversion process may beapplied to a process for the conversion of alkanes to higher liquidhydrocarbons. In an embodiment, natural gas (or another hydrocarbonfeedstock) and molecular bromine may be carried by separate lines 601,602 into a heated bromination reactor 603 and allowed to react.Bromination products may include, but are not limited to, HBr, alkylbromides, olefins, and possibly unreacted hydrocarbons. The brominationproducts may exit the reactor and be carried by a line 604 into a firstseparation unit 605, where monobrominated hydrocarbons and HBr may beseparated from polybrominated hydrocarbons. In some embodiments, thepolybromides may be carried by a line 606 back to the brominationreactor, where they may undergo reproportionation with methane and/orother light hydrocarbons, which may be present in the natural gas and/orintroduced to the bromination reactor. Light gases such as ethane,propane and butane may be carried by line 621 and may be allowed reactwith bromine in a light hydrocarbon bromination reactor 615 to producealkyl halides and HBr.

In the embodiment shown in FIG. 27, any unreacted hydrocarbon feedstock,HBr, monobromides, and any olefins formed in the bromination reactor maybe carried by a line 607 to coupling reactor 609, where themonobromides, olefins, or any combination thereof may react in thepresence of a coupling catalyst to form higher hydrocarbons. In anembodiment, a heat exchanger 608 may be used to adjust the temperatureof the brominated products stream 607 to a desired inlet temperature tothe coupling reactor 609. The coupling reactor products may include HBr,higher hydrocarbons, unreacted hydrocarbons, alkyl bromides, or anycombination thereof. The coupling reactor products may exit the couplingreactor 609 and be carried by a line 610 to an HBr separation unit 612.The coupling reactor products may pass through another heat exchanger611 as necessary to adjust the temperature of the coupling productsstream to a desired inlet temperature to the HBr separation unit 612.HBr can be separated from the hydrocarbons using a number of differentmethods as previously described herein. For example, HBr may be separateusing pressure-swing absorption, temperature-swing absorption,temperature-swing adsorption, membrane-based separation, distillation,or any combination of separation techniques, or another suitableseparation technology. Specific descriptions of these technologies areincluded herein.

The liquid hydrocarbon products may then be carried by a line 16 to aproduct clean-up unit 613, to yield final hydrocarbon products 617.After HBr is separated from the hydrocarbon products and any lighthydrocarbons that may be present in the HBr separation unit 612, thelight hydrocarbons may be carried by a line 618 into a second separationunit 619, which may employ pressure- or temperature-swing adsorption,membrane-based separation, cryogenic distillation or any other suitableseparation technology. Methane may be returned to the brominationreactor 604 via one or more line 620 and other light hydrocarbons may bereturned to the lights bromination reactor 615 via line 621.Alternately, the light gases may be added to the downstream zone of thebromination reactor where they may reproportionate with polybromides toform the corresponding alkyl bromides.

The HBr stream that evolves from the HBr separation unit 612 may becarried by a line 622 to a bromine generation unit 623. Air or oxygenmay be fed into the unit through line 624. Bromine may regenerated byreacting HBr with oxygen in the presence of a suitable catalyst such asan aqueous solution of selenium bromide or oxybromides (SeOBr₂, Se₂Br₂,etc.), as described above.

The resulting stream 625 from bromine generation reactor 623 may containwater, molecular bromine, oxygen, nitrogen, and possibly other gases ifair was used as the source of oxygen. This product stream 625 may becarried through a heat exchanger system 626 into a flash vaporizationunit 627, which may separate most of the molecular bromine from water,oxygen, nitrogen, and other gases that are present. Molecular brominecontaining no more than a trace of H₂O, either as a liquid or vapor, maybe carried by a line 628 to a heat exchanger 629, and then returned tothe bromination reactor 603, the lights bromination reactor 615, orboth.

Water from the flash vaporization unit (containing up to about 3% byweight of molecular bromine) may be sent by a line 630 to a distillationunit 631, which may yields water as the bottoms stream and bromine orbromine-water azeotrope as a distillate. The distillate may be returnedthrough a line 632 back to the flash vaporization unit. An embodiment ofthis invention may utilize pH control in the distillation column 631 toprevent the hydrolysis reaction between water and bromine. Thehydrolysis reaction may produce HBr, which may be lost in the bottomsstream of the distillation column in the absence of pH control. A pH oflower than about 3 may be desired to reduce or eliminate the hydrolysisreaction. Conventional acids such as sulfuric acid, hydrochloric acid,or phosphoric acid may be used for pH control.

The gaseous products of the flash vaporization unit may contain no morethan a minor or trace amount of bromine and may carried by a line 633 toa bromine scavenging unit 634, which may separate molecular bromine fromthe other gases. As described above, adsorbents or reactants capable ofcapturing bromine may be used for bromine scavenging.

Another embodiment of the process for converting gaseous alkanes intoliquid hydrocarbons utilizing the conversion of HBr into elementalbromine in the presence of selenium or tellurium is shown in FIG. 28. Inthis process configuration, the operating pressure of the Br₂ generationunit 623 may be greater than the pressure in the bromination reactor603. As in the previous case, stream 625 from bromine generation reactor623 may contain water, molecular bromine, oxygen, nitrogen, and possiblyother gases if air was used as the source of oxygen. This product stream625 may be carried through a heat exchanger system 626 into a flashvaporization unit 627, which may separate most of the molecular brominefrom water, oxygen, nitrogen, and any other gases that may be present.Liquid molecular bromine, containing no more than a trace of H₂O, may becarried by a line 628 to a heat exchanger 629, and then returned to thebromination reactor. Water from the flash vaporization unit, which maycontain up to about 3% by weight of molecular bromine, may be sent by aline 630 to a distillation unit 631, which may yield water as thebottoms stream and bromine or bromine-water azeotrope as a distillate.The distillate may be returned through a line 632 back to the flashvaporization unit.

The gaseous products of the flash vaporization unit may be returned tothe bromination reactor 603, the lights bromination reactor 615, orboth. In this embodiment, the bromination reactor 603, the polybromideseparation unit 605, the lights bromination reactor 615, and thecoupling reactor 609 may be the same as in the previous embodiment,except that all product and feed streams, with the exception of stream606, may also contain N₂.

The coupling product stream 610, which may contain hydrocarbons, HBr,and N₂, may be cooled in heat exchanger 611, and then go to the HBrseparation unit 612. The HBr separation unit 612 may selectivelyseparate HBr from the other components and transport the HBr via line622 to the bromine generation unit 623. A number of different methodsmay be used to achieve the desired separation (e.g., distillation,adsorption, etc.). In some embodiments, temperature swing absorption maybe used to separate the HBr from the coupling products stream, asdescribed above.

Stream 718, which may contain only hydrocarbons and N₂, may betransported to a product recovery unit 719. The product recovery unit719 may produce a liquid hydrocarbon product stream 616, which may besent to a product cleanup unit 613 to yield the final hydrocarbonproducts 617; a light gases stream 621 containing primarily C₃ and C₄hydrocarbons, which may be further refined to product LPG product orsent to lights bromination unit 615; and a gas stream 736, which maycontain N₂, unconverted CH₄, and possibly some C₂ and C₃ hydrocarbons.The gas stream 736 may be used as fuel for generating any energy (e.g.,heat, electricity, etc.) that may be required for the process.

A number of different methods may be used to achieve the desiredseparation in the product recovery unit 719. In some embodiments, aheavy organic solvent (either a pure component (e.g., C₁₂H₂₆) or amixture (e.g., diesel)) may be used to absorb all the C₅ and heavierhydrocarbons, along with significant amounts of C₄ and C₃ hydrocarbonspresent in stream 718. A distillation sequence may then be used torecover the liquid hydrocarbon product and light gases (e.g., C₄ and C₃hydrocarbons) from the solvent, which may then be recycled to theabsorber. Any C₄ and lighter hydrocarbons may be recovered from the gasstream leaving the absorber using techniques such as cryogenicdistillation, expansion cooling, absorption, membrane,pressure/temperature swing adsorption, etc.

This embodiment may allow the bromine scavenging unit to be eliminatedand allow cooling water, rather than brine or refrigeration, to be usedin the flash separation unit 627. However, due to the presence of N₂,the bromination reactor 603, the polybromide separation unit 605, thelights bromination reactor 615, and the coupling reactor 609 may belarger. This embodiment may be economically attractive for small scaleprocesses such as those producing less than about 3,000 barrels ofliquid hydrocarbons per day. In another embodiment, this embodiment maybe attractive for processes producing less than about 2,000 barrels perday.

Another embodiment of the process is shown in FIG. 29. Due to thedifficulty in obtaining a high purity HBr stream with a high recovery asa result of the VLE behavior of ethane-HBr and HBr-propene, a differentseparation process may be used to remove HBr from the coupling productsstream 610. In this embodiment, the cooled coupling product stream 610,which may contain hydrocarbons and HBr, may be separated to yield avapor stream 822 containing HBr, C₃, and lighter hydrocarbons; a liquidhydrocarbon stream 616; and a C₄ hydrocarbon stream 818, which may alsocontain some C₃ as well. A number of different methods may be used toachieve the separation including, but not limited to, distillation, asolvent absorption based process, or both. Stream 822 may be transportedto the bromine generation unit 623 where HBr may be converted to Br₂ inthe presence of selenium or tellurium, as described above. The lighthydrocarbons may pass through the process unreacted. Stream 625 frombromine generation reactor 623 may contain water, molecular bromine,oxygen, nitrogen if air was used as the source of oxygen, and any C₃ andlighter hydrocarbons that entered the bromine generation reactor. Theproduct stream 625 may be carried through a heat exchanger system 626into a flash vaporization unit 627, which may separate most of themolecular bromine from the water, oxygen, nitrogen, and any lighthydrocarbons that may be present. Liquid molecular bromine containing nomore than a trace of H₂O may be carried by a line 628 to a heatexchanger 629, and then returned to the bromination reactor 603, thelights bromination reactor 615, or both. Water from the flashvaporization unit containing up to about 3% by weight of molecularbromine may be sent by a line 630 to a distillation unit 631, which mayyield water as the bottoms stream and bromine or bromine-water azeotropeas a distillate. The distillate may be returned through a line 632 backto the flash vaporization unit.

The gaseous products of the flash vaporization unit (e.g., oxygen,nitrogen, light hydrocarbons, and no more than a minor or trace amountof bromine) may be carried by a line 633 to a bromine scavenging unit634, which may separate molecular bromine from any other gases present.Any of the techniques described above may be used for brominescavenging. The recovered bromine may be carried by a line 365 through aheat exchanger 629 and reintroduced into the bromination reactor 603,the lights bromination reactor 615, or both. The remaining gases, whichmay include oxygen, nitrogen, and light hydrocarbons, may be transportedvia line 837 to a separation unit 819, where any hydrocarbons including,but not limited to, C₂, C₃, and heavier hydrocarbons, may be recoveredand sent, along with stream 818, to lights bromination reactor 615. Theremaining gases including, but not limited to oxygen, nitrogen, methaneand some light hydrocarbons, may be used as fuel for generating energyfor the process. Any standard separation technology including, but notlimited to, distillation, expansion cooling, absorption, membrane, andpressure/temperature swing adsorption, may be used to achieve thedesired separation.

Continuous Flow Zone Reactor Configurations (CFZR)

In an embodiment that utilizes a solid reactant to capture hydrogenhalide, a continuous flow zone reactor (hereinafter CFZR) may be used tocarry out the method of converting hydrocarbon feedstocks into usefulproducts. The CFZR comprises of two or more zones in which the solidcatalyst particulates (e.g., comprising cataloreactants) may betransported between the zones by gravity, pneumatic conveyance, or anyother direct transport means as are known in the art for fluidized ormoving bed reactor designs, or any combination thereof. An embodiment ofthe CFZR is shown in FIG. 30 with a plurality of reactor zones. Thesolid reactant particles may react with hydrogen halide (e.g., HBr) inthe hydrogen halide neutralization zone 910 to make water and metalbromide, which may pass along with the products and any inert gases inthe outlet stream 912 to a products separation sub-process 914, asdescribed in more detail above. The catalytic solids may leave theneutralization zone as a metal bromide stream 916. In order to preventhydrogen halide breakthrough in the neutralization zone, the solidsflowrate may contain a metal oxide in an amount exceeding thestoichiometric requirement to neutralize the entering hydrogen halide.As a result, the metal bromide stream 916 leaving the hydrogen halideneutralization zone 910 may comprise metal bromide and metal oxide.

As shown in FIG. 30, the metal bromide stream 916 may be heated in aheating zone 918 using any known method for heating a solid particulate.Non-limiting examples may include heat transfer through direct contactwith inert gases or by indirect contact through heat transfer tubes in afluidized bed. The resulting heated metal bromide stream 920 may leavethe heating zone 918 and pass into a bromine generation reactor 922. Themetal bromide, which may contain some metal oxide, may be contacted withan air or oxygen stream 936 to generate elemental bromine in the brominegeneration reactor 922. Any residual hydrocarbons or brominatedhydrocarbons adsorbed on the solid catalyst may also be oxidized bycontact with air. The combustion products may include CO₂, N₂, andpotentially some trace hydrogen halide. These products may pass out ofthe bromine generation reactor 922 as a bromine stream 924, which maypass to a bromination reactor 926 for use in the formation of alkylbromides, as described in more detail above. Upon contact with the airor oxygen source, the metal bromide may be converted to a metal oxidefor reuse in the process. Depending on the reaction conditions, themetal oxide stream 930 may comprise some solid catalyst as a metalbromide in order to avoid oxygen breakthrough into the bromine stream924.

The metal oxide stream 930 leaving the bromine generation reactor may beconveyed to a cooling zone 928, where the catalyst may be cooled usingany known method for cooling a solid particulate. Non-limiting examplesmay include heat transfer through direct contact with inert gases or byindirect contact through heat transfer tubes in a fluidized bed. Thecooled metal oxide stream 932 may then pass out of the cooling zone 928and into the hydrogen halide neutralization zone 910 to complete thesolid catalyst recycle loop. An optional metal oxide storage vessel 934may be utilized before or after the cooling zone to store the metaloxide solid reactant prior to metering a desired amount back into theprocess. In an embodiment utilizing a storage vessel, the storage vesselmay be capable of storing the entire amount of metal oxide in the eventof a process shutdown.

In the embodiment shown in FIG. 30, both bromine generation reactor 922and the hydrogen halide neutralization zone 910 may be adiabaticreactors. The HBr neutralization zone 910 may be a dense moving bed or afluidized bed reactor, or a combination of both. The Bromineregeneration reactor may be either a dense moving bed reactor, afluidized bed reactor, or a combination of both. The moving bed reactorsmay be configured with gas flowing upward against the flow of solids, ordownward, parallel to the flow of solids. Solid flow from each reactormay be regulated by a looping seal valve, a rotary valve, or by othermechanical means. Although FIG. 30 shows a particular vertical alignmentof the zone reactor, other configurations are feasible.

In another embodiment of the CFZR, an additional gas stream (not shownin FIG. 30) may also be added to the neutralization zone 910. Thisstream may be substantially hydrogen halide free, and may be primarilycomposed of light gases such as N₂, methane and other light hydrocarbons(e.g., C₂, C₃, and C4). In addition is may also include water and smallamounts of higher hydrocarbons (C₅ ⁺). The purpose of this stream is toreduce the temperature rise in the neutralization zone, and this streammay be either added directly to the neutralization zone, or mixed withthe feed stream to the neutralization zone. This stream may be externalto the system, or it may be an appropriate stream from another part ofthe system (e.g., an appropriate gas stream in the separationsub-process). This embodiment may improve the economics of the entireprocess by reducing or eliminating the cooling load in cooling sectionof the CFZR and transferring it to the product recovery system. This mayresult in a process with a lower capital cost as the materials ofconstruction used for the heat transfer surfaces in the CFZR may besignificantly more expensive than those used in the product recoverysystem due to the presence of a hydrohalic acid. In addition, thisembodiment also decreases the change in the temperature of the catalyticsolids as it passes through the different zones of the CFZR, which mayin turn increase the overall life of the catalytic solid.

Other embodiments may also be possible. For example, the solid catalyticreactant may remain stationary, while moving the zone from one locationto the next, in a continuous loop, in the configuration of a simulatedmoving bed. In this embodiment, a series of control valves may be usedto sequentially direct flow from one zone to the next. This has theadvantage of near continuous operation without the additional complexityof moving the solids between zones. In a similar manner, the zonereactor may be configured as rotating wheel, in which case the solidsmay be moved in a dense plug from one location to another in tangentialmovement. The gases in each zone are fed continuously, while solids arepushed from one zone to the next in a circular pathway around the wheel.

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, thescope of the invention.

Example 1 Reproportionation of Dibromomethane with Propane

Methane (11 sccm, 1 atm) was combined with nitrogen (15 sccm, 1 atm) atroom temperature via a mixing tee and passed through a room temperaturebubbler full of bromine. The CH₄/N₂/Br₂ mixture was plumbed into apreheated glass tube at 500° C., and bromination of the methane tookplace with a residence time (“t_(res)”) of 60 seconds, producingprimarily bromomethane, dibromomethane, and HBr. The stream of nitrogen,HBr, and partially brominated hydrocarbon was combined with propane(0.75 sccm, 1 atm) in a mixing tee and passed into a second glassreactor tube at 525° C. with a residence time (“t_(res)”) of 60 s. Inthe second reactor tube, polybrominated hydrocarbons (e.g., CH₂Br₂,CHBr₃) react with the propane to produce bromopropanes. Thereproportionation is idealized by the following reaction:

CH₂Br₂+C₃H₈→CH₃Br+C₃H₇Br

As products left the second reactor, they were collected by a series oftraps containing 4 M NaOH (which neutralized the HBr) and hexadecane(containing octadecane as an internal standard) to dissolve as much ofthe hydrocarbon products as possible. Volatile components like methaneand propane were collected in a gas bag after the HBr/hydrocarbon traps.All products were quantified by gas chromatography. The results (“Ex.1”) are summarized in Table 1. For comparison, the reactions were alsorun with two reactors, but without reproportionation with propane(“Control A”), and with only the first reactor and without propane(“Control B”).

TABLE 1 Reproportionation of Dibromomethane Ex. 1 (bromination/ ControlA Control B reproportionation) (bromination) (bromination) Brominationt_(res) 60 60 60 Reproportionation t_(res) 60 60  0 CH₄ conversion 40%47% 45% CH₃Br/(CH₃Br + 93% 84% 74% CH₂Br₂) C₃H₈ conversion 85% N/A N/ACarbon balance 96% 97% 96%

Example 2 Separation of Anhydrous HBr

20 ml stock HBr aqueous solution were added to 20 g CaBr₂H₂O followed byheating to 70° C. A significant evolution of HBr gas was observed(determined by AgNO₃ precipitation and the NH₃ fuming test). Thereleased HBr was not quantified as the reaction was carried out in anopen vessel.

Example 3 Separation of Anhydrous HBr

Dehydration with H₂SO₄ was attempted by adding a concentrated solutionof H₂SO₄ to HBr. Qualitative tests were conducted in which differentconcentration of H₂SO₄ were added to HBr for determination of thethreshold concentration where oxidation of HBr no longer occurs:2HBr+H₂SO₄→Br₂+SO₂+2H₂O

It was determined that the H₂SO₄ concentration below which no oxidationis apparent is about 70 wt. %. 30 ml 70% H₂SO₄ was added to 30 ml stockHBr azeotrope (48 wt. %) and the mixture was heated to boiling. The HBrcontent was determined quantitatively by AgNO₃ precipitation andgravimetric determination of AgBr from a solution aliquot at the momentof mixing, after 15 min and after 30 min boiling.

Example 4 Metathesis of Brominated Methane Over Selected Catalysts

A series of experiments were conducted in which methane was brominatedin a manner substantially the same as or similar to that described inExample 1 (10 sccm methane bubbled through room temperature bromine,followed by passage of the mixture through a reactor tube heated to 500°C.), and the bromination products were then passed over variousmetal-ion exchanged or impregnated zeolite catalysts, at atmosphericpressure (total pressure), at a temperature of from 350° C. to 450° C.,with a residence time of 40 seconds. Table 2 summarizes the distributionof metathesis products. Catalysts are denoted by metal ion (e.g., Ba,Co, Mn, etc.) and by type of Zeolyst Int'l. zeolite (e.g., 5524, 58,8014, etc.). The mass (mg) of each product, as well as the total mass ofproducts is given for each run. The abbreviations, B, PhBr, T, X, and Mrefer to benzene, phenyl bromide, toluene, xylene, and mesitylene,respectively.

TABLE 2 Metathesis of Brominated Methane Over Selected Catalysts Total T(C.) Catalyst B PhBr T X M (mg) 350 Ba 5524 0.25 0 0.96 2.58 3.14 6.93350 Ba 58 0.31 0 1.48 3.2 3.11 8.11 350 Ba 8014 0.3 0 1.3 2.87 3.15 7.6350 Ca 58 0.2 0 0.81 2.44 3.09 6.53 350 Co 2314 1.22 0.02 3.05 2.18 0.567.04 350 Co 3024 0.36 0 2.06 4.21 3.47 10.1 350 Co 58 0.2 0 1.05 2.913.34 7.5 350 Mg 3024 0.31 0 1.53 3.59 3.89 9.32 350 Mg 58 0.28 0 1.413.3 3.43 8.42 350 Mn 2314 1.07 0.03 2.86 2.26 0.65 6.86 350 Mn 3024 0.530 2.92 4.8 3.02 11.27 350 Mn 58 0.17 0 0.88 2.7 3.62 7.37 350 Ni 23141.12 0.05 2.94 2.44 0.74 7.29 350 Ni 3024 0.61 0 2.82 3.85 2.13 9.41 375Ba 5524 0.32 0 1.32 2.82 2.57 7.04 375 Ba 58 0.4 0 1.84 2.93 2.4 7.57375 Ba 8014 0.32 0 1.23 2.84 2.95 7.34 375 Ca 58 0.2 0 0.96 2.55 2.936.64 375 Co 3024 0.47 0 2.3 3.52 2.18 8.48 375 Co 58 0.3 0 1.54 2.832.42 7.1 375 Mg 3024 0.37 0 1.81 3.26 2.78 8.22 375 Mg 58 0.34 0 1.673.04 2.74 7.8 375 Mn 3024 0.62 0 2.91 3.9 2.17 9.59 375 Mn 58 0.22 01.18 2.71 2.83 6.94 375 Pd 2314 1.54 0 3.1 1.83 0.37 6.85 400 Ba 55240.46 0 2.37 4.16 2.95 9.94 400 Ba 58 0.7 0 3.15 3.91 2.7 10.47 400 Ba8014 0.38 0 1.57 3.81 3.77 9.53 400 Ca 58 0.41 0 1.89 3.43 2.81 8.54 400Co 3024 0.78 0 3.42 4.14 2.26 10.6 400 Co 58 0.62 0 2.71 3.36 2.31 8.99400 Mg 3024 0.76 0 3.26 4.11 2.64 10.76 400 Mg 58 0.71 0 3.04 3.74 2.5910.08 400 Mn 3024 0.98 0 4.1 4.38 2.06 11.52 400 Mn 58 0.48 0 2.26 3.442.64 8.82 400 Ni 3024 0.81 0 3.15 3.35 1.72 9.04 400 Pb 2314 1.2 0.033.25 3.27 1.2 8.94 400 Pb 3024 1.07 0.04 2.77 3.63 1.66 9.17 400 Pd 23142.44 0 3.16 1.22 0.18 7.01 400 Sr 2314 2.13 0.01 4.05 2.29 0.46 8.94 400Sr 3024 1.93 0.05 4.03 2.67 0.65 9.32 425 Ag 3024 2.79 0.02 4.16 1.780.29 9.04 425 Ag 8014 3.09 0.02 3.52 1.09 0.16 7.88 425 Ba 5524 0.54 02.67 3.67 2.33 9.22 425 Ba 58 0.79 0 3 2.94 1.75 8.48 425 Bi 2314 3.130.03 4.47 1.61 0.23 9.48 425 Co 2314 3.39 0.03 4.34 1.59 0.25 9.6 425 Co3024 1.07 0 3.42 2.79 1.09 8.38 425 Cu 2314 2.89 0.02 4.74 2.13 0.3710.15 425 Li 5524 1.51 0.04 3.31 3.27 1.12 9.24 425 Mg 3024 0.99 0 3.282.85 1.37 8.48 425 Mg 58 0.81 0 2.62 2.16 1.11 6.7 425 Mn 3024 1.22 03.9 3.01 1.14 9.27 425 Mo 2314 3.06 0.04 4.02 1.46 0.24 8.82 425 Ni 30240.97 0 3.38 2.85 1.32 8.51 425 Sr 3024 2.53 0.02 4.36 2.22 0.43 9.56 450Ag 3024 3.84 0.02 4.27 1.36 0.18 9.67 450 Bi 2314 3.9 0.01 3.59 0.670.06 8.23 450 Ca 2314 3.64 0.02 4.1 1 0.16 8.92 450 Co 2314 4.12 0.013.77 0.77 0.08 8.75 450 Cu 2314 3.65 0 4.3 1.1 0.14 9.19 450 Fe 23144.42 0.02 3.43 0.74 0.09 8.69 450 Fe 3024 3.61 0.01 2.96 0.63 0.08 7.28450 Fe 5524 3.99 0.03 3.63 0.85 0.11 8.6 450 La 2314 3.48 0.01 3.81 0.870.12 8.29 450 Li 8014 1.74 0.02 2.61 2.67 0.84 7.89 450 Mg 2314 4.2 0.023.84 0.76 0.1 8.92 450 Mn 2314 3.78 0.02 3.9 0.88 0.12 8.7 450 Mo 23143.88 0.01 3.26 0.58 0.06 7.79 450 Ni 2314 4.39 0.01 3.12 0.44 0.03 8 450Pb 2314 2.58 0.01 4.68 2.31 0.45 10.02 450 Pb 3024 2.08 0.01 4.44 2.870.7 10.1 450 Pb 5524 1.89 0.02 3.58 2.71 0.73 8.93 450 Pd 2314 4.03 01.58 0.14 0 5.76 450 Sr 2314 3.71 0 4.78 1.68 0.21 10.39 450 Sr 30242.51 0.01 3.76 1.61 0.26 8.14

Example 5 Hydrodehalogenation of Bromobenzene, And Catalyst Regeneration

A test solution (1.5 ml/hr), which includes 1.9 wt % bromobenzene (PhBr)dissolved in dodecane, diluted by N₂ (1.1 ml/min) was fed into a tubularquartz reactor in which 3.6 g of highly dispersed precious metalcatalyst (Pd/Al₂O₃, 0.5 wt %) was loaded. The reaction was carried outat 325° C. with a residence time of 15 s. The reaction effluent wastrapped in a bubbler with 8 ml 4M NaOH solution pre-added. The carriergas as well as the gaseous product were collected in a gas bag. All ofthe carbon-based products in the gas phase and oil phase in the liquidproduct were subjected to GC analysis. For the base trap solution, theHBr concentration was measured with an ion-selective electrode. Based onall of these measurements, carbon and bromine balances were calculated.

The experiment was continuously run for over 300 hours until theconversion of PhBr dropped from 100% in the initial 70 hrs to below 30%(FIG. 31). Hydrodebromination of PhBr took place over the catalyst bedwith the formation of benzene (“BZ”) and HBr as the major products,accompanied with some light hydrocarbons (C₃-C₇) being detected asbyproducts, which originated from solvent decomposition. Carbondeposition was recognized as the primary reason for deactivation of thecatalyst. The catalyst proved to be re-generable via decoking at 500° C.with O₂ oxidation (5 ml/min) for 10 hrs, followed by H₂ reduction (20ml/min) at 400° C. for 3 hrs. The regenerated catalyst was identified tobe as effective as the fresh catalyst, as confirmed by its ability tocatalyze the same hydrodebromination reaction without activity loss inthe first 70 hours (FIG. 32).

Example 6

The gas flow rate inlet to the HBr absorption process is 700,000 m³/h ata temperature of 50° C. and includes HBr and hydrocarbons. The molarconcentration of HBr is more than 70% of the feed mixture. The gas isfed to an absorption column that is cooled externally with liquidrecirculation through a heat exchanger. The liquid inlet to theabsorption column is an aqueous HBr stream also at a temperature of 50°C. and has a flowrate of 7,600,000 kg/h, with the HBr concentration of50% by weight. The liquid outlet stream from the HBr absorption columnhas a flow rate of 10,800,000 Kg/h with a HBr concentration of 65% byweight. The liquid outlet is then sent to the evaporation section where3,200,000 kg/h of HBr is recovered by heating the liquid stream to atemperature of 120° C. The liquid outlet from the evaporator is returnedto the absorption column. Two absorption columns are required in theexemplary embodiment, each with a diameter of 8 meters and a height of 8meters. Packing material can be used in the column to improve theabsorption process.

Example 7

The gas flow rate inlet to the HBr absorption process is 700,000 m³/h ata temperature of 100° C. and includes HBr and hydrocarbons. The molarconcentration of HBr is more than 70% of the HBr and hydrocarbons feedmixture. A distillation scheme is used to separate HBr fromhydrocarbons. The distillation system operates at a pressure between 10atm and 30 atm. A first distillation column separates methane and C₂from the rest of the components and requires 24 theoretical stages. Thecondenser duty for this column is 310 MMkcal/h and the condensertemperature is −35° C. The reboiler duty is 112 MMkcal/h and thereboiler temperature is −7° C. A second distillation column separatesmethane from C₂ and HBr. The bottoms stream consists of C₂ with a smallamount of HBr. This column requires 18 theoretical stages. The thirddistillation column separates HBr from other components heavier thanHBr. The distillate is HBr with more than 99% purity. This columnrequires 37 theoretical stages. The condenser duty for the column is 290MMkcal/h and the condenser temperature is −9° C. The reboiler duty is440 MMkcal.h and the reboiler temperature is −36° C. The fourthdistillation column separates light gases from the rest of thecomponents and requires 10 theoretical stages. The condenser duty forthis column is 30 MMkcal/h and the condenser temperature is −28° C. Thereboiler duty is 65 MMkcal/h and the reboiler temperature is 233° C.

Example 8

The gas outlet from the coupling reactor has HBr weight fraction of 72%.This stream is cooled down to 29° C., and vapor-liquid flash separationis used to remove heavy hydrocarbons. The vapor outlet from the flash isat a pressure of 3 atm and a flow rate of 26870 m3/hr. The aq. HBr inletto the absorption column has 52% HBr by weight and a flow rate if 339512kg/hr. The concentrated HBr at the bottom of the absorption column has65% HBr by weight and a flow rate of 471950 kg/hr. Eight stages arerequired for the absorption column. The concentrated HBr stream is sentto a stripper where the column with six stages operates at a pressure of15 atm. The reboiler temperature is 187° C. Dehydrated HBr leaves thetop of the stripping column with 99% HBr by weight with 1% water byweight and the bottoms stream of the stripper consists of Aq. HBr with52% HBr by weight and is returned back to the absorption column.

Example 9 Bromine Recovery Using Chilled Brine

The test setup consisted of three test vessels that were connected inseries. The first contained liquid bromine at 15° C. and atmosphericpressure. The second contained a brine solution consisting of 100 ml of24.7% by weight NaCl in water. The third vessel contained 30 ml of 4 MNaOH as a bromine trap to capture any bromine passing through thechilled brine vessel. A nitrogen carrier stream was introduced into thebottom of the bromine vessel at 10 sccm and allowed to bubble throughthe liquid bromine. The bromine partial pressure at this temperature was0.18 atm. The nitrogen and bromine then passed in series to the bottomof the chilled brine and sodium hydroxide solutions in order to ensureproper gas to liquid contact.

Three tests were conducted using the test setup. The first test wasconducted using a chilled brine at a temperature of −5° C. with abromine flow for 3 hours. The second test used a chilled brine at −10°C. and was conducted for 2.5 hours. The results of the first twoabsorption tests are shown in Table 3. The last test measured theabsorption characteristics of the system over time. This test measuredthe absorption amounts at six times over a 12 hour absorption run. Theresults of the 12 hour absorption test are shown in Table 4a. Brominebreakthrough to the NaOH trap increases with time on stream as shown inTable 4b. This is a result of saturating the brine solution withbromine, thereby, reducing the capture capacity of the chilled brine.

TABLE 3 Br₂ Recovery Using Chilled Brine Br₂ Absorbed Br₂ Distribution(g/hr-L) (%) Brine at −5° C. (Trapping for 3 hr) Brine 7.6 95.1 NaOH 0.44.9 Br Balance (%) 94.5 Brine at −10° C. (Trapping for 2.5 hr) Brine 7.998.5 NaOH 0.1 1.5 Br Balance (%) 92.2

TABLE 4a Average Br₂ Recovery Using Chilled Brine Br₂ Absorbed Br₂Distribution (g/hr-L) (%) Brine at −5° C. (Trapping for 12 hr) Brine 7.888.1 NaOH 1.1 11.9 Br Balance (%) 101.3

TABLE 4b Time Dependence of Bromine Breakthrough in Base Trap Brominebreakthrough Time Percentage in base Trap 0-2 2.5 2-4 7.5 4-6 9.3 6-813.9  8-10 19.6 10-12 19.6

Example 10

In this example, 0.5 g SeO₂ was loaded into two bubbler containers. A3.06 ml 48 wt. % aqueous HBr solution (2.187 g HBr, 4.56 g soln.) wasadded in the first container, and a 4.08 ml of the same solution (2.917g HBr, 6.08 g soln.) was added in the second container at roomtemperature. The samples were submerged in a preheated oil bath at 100°C. A 3 ml/min. oxygen stream was passed over the containers with the gasleaving the containers passed through 15 ml 4 M NaOH solution thatcaptured all bromine vapors. The NaOH traps were changed every hour andthe bromine content was determined by iodometric titration with standard0.1000 M Na₂S₂O₃. The results are shown in Table 5 below.

TABLE 5 mol mol mmol mmol Time, Sam- Sam- Br/ Br/ Br₂/ Br₂/ h ple 1 ple2 hour(1) hour(2) ml*min(1) ml*min(2) 1 7.6 6.97 0.00076 0.0006970.002069717 0.001424 2 7.82 5.4 0.000782 0.00054 0.00212963 0.001103 34.35 2.78 0.000435 0.000278 0.001184641 0.000568 4 3.92 7 0.0003920.0007 0.001067538 0.00143 5 4.3 5.5 0.00043 0.00055 0.0011710240.001123 6 3.28 4.58 0.000328 0.000458 0.000893246 0.000935 7 3.7 5.090.00037 0.000509 0.001007625 0.00104

Example 11

In this example, 1 g SeO₂ was loaded into two bubbler containers. A 3.06ml, 62 wt. % aqueous HBr solution was added to the first one (2.915.6 gHBr, 4.7 g soln.), and 3.67 ml of the same solution to the second one(3.645 g HBr, 5.88 g soln.) at room temperature. The samples weresubmerged in a preheated oil bath at 100° C. A 3 ml/min. oxygen streamwas passed over the containers with the gas leaving the containerspassed through 15 ml 4 M NaOH solution that captured all bromine vapors.The NaOH traps were changed every hour and the bromine content wasdetermined by iodometric titration with standard 0.1000 M Na₂S₂O₃. Theresults are shown in Table 6 below.

TABLE 6 mol mol mmol mmol Time, Sam- Sam- Br/ Br/ Br₂/ Br₂/ h ple 1 ple2 hour(1) hour(2) ml*min(1) ml*min(2) 1 16.8 20 0.00168 0.002 0.0046670.004505 2 16.24 17.58 0.001624 0.001758 0.004511 0.003959 3 12.65 150.001265 0.0015 0.003514 0.003378 5 15.89 16.7 0.001589 0.00167 0.0044140.003761

Example 12

In this example, 1 g SeO₂ was loaded into two bubbler containers. A 5.12ml, 68 wt. % aqueous HBr solution was added to the first one (5.83 gHBr, 8.81 g soln.), and 7.16 ml of the same solution to the second one(7.29 g HBr, 12.60 g soln.) at room temperature. The samples weresubmerged in preheated oil bath at 100° C. A 3 ml/min. oxygen stream waspassed over the containers with the gas leaving the containers passedthrough 15 ml 4 M NaOH solution that captured all bromine vapors. TheNaOH traps were changed every hour and the bromine content determined byiodometric titration with standard 0.1000 M Na₂S₂O₃. The results areshown in Table 7 below.

TABLE 7 mol mol mmol mmol Time, Sam- Sam- Br/ Br/ Br₂/ Br₂/ h ple 1 ple2 hour(1) hour(2) ml*min(1) ml*min(2) 1 45.6 53.63 0.00456 0.0053630.0076 0.006242 2 28.05 55.9 0.002805 0.00559 0.004675 0.006506 3 16.1333.2 0.001613 0.00332 0.002688 0.003864 4 15.2 22.31 0.00152 0.0022310.002533 0.002597

Example 13

In this example, 1 g SeO₂ was loaded in a bubbler container. A 5 ml, 68wt. % aqueous HI solution was added to the bubbler container (5.83 g HI,8.81 g soln.) at room temperature. The sample was submerged in preheatedoil bath at 100° C. A 3 ml/min. oxygen stream was passed over thecontainer with the gas leaving the container passed through 15 ml 4 MNaOH solution that captured all iodine vapors. The NaOH traps werechanged every hour and the iodine content determined by titration withstandard 0.1000 M Na₂S₂O₃.

Example 14

In this example, three samples of 20 grams of H-exchanged zeolite wasrefluxed at 100° C. with 300 mL 0.1 M, 1 M and saturated H₂C₂O₄ (˜1.15M) correspondingly for 2 hours. The zeolite was filtered, washed anddried slowly. The resulted ZSM-5 modified materials were exchanged with0.1 M Mn(NO₃)₂ for at least eight hours, filtered, washed and dried. Thethree samples were tested for coupling of methyl bromide at 425° C. witha residence time of 3 seconds. The data is summarized in Table 8 shownbelow.

TABLE 8 Benzene/ BTX, Coke, C-Bal. [H₂C₂O₄], Catalyst BTX, % % % % mol/lMn3024_0 19.1 39.4 5.4 97.9 N/A De-Al Mn3024_1 25.5 42.4 5.4 94.7 0.1De-Al Mn3024_2 26.7 41.5 5.2 94.6 1.0 De-Al Mn3024_3 30.8 40.8 6.5 93.61.15

Example 15

In this example, the effect of water vapors on the catalytic conversionof methyl bromide conversion to BTX products using conditions typicalfor a BTX process (425° C., 0.5 atm. methyl bromide partial pressure, 5s residence time) were examined. The results are summarized below inTable 9, showing the trend of the coke generated as a function of wateradded. It is important to note that the products distribution isrelatively unchanged by the water addition to the reaction mixture.

TABLE 9 T Bubbler (° C.) None 0 10 19 36 58 % H₂O 0.0 0.3 0.6 1.0 2.98.3 % C Bal 100 98.2 103.4 100.1 107.5 105.9 % MeBr 99.0 99.3 99.4 99.299.3 99.2 Conv. % Coke 7.4 6.7 5.5 6.3 4.8 4.5 % BTX 35.8 36.6 34.8 34.332.8 32.2 % B/BTX 19.6 21.3 20.8 19.0 18.4 16.1 % C2-C6 41.5 42.3 45.345.1 49.8 50.4 % MDN+ 13.5 13.2 13.4 13.0 11.4 11.5

Example 16

In this example, a modified ZSM-5 catalyst was used to producemesitylene from methylbromide. 1.0 gram of 7% CuO/0.5% ZnO impregnatedZSM-5 catalyst was loaded into a test cell with operating conditions asfollows: a reaction temperature of 400° C., a reaction time of 1 hour, aresidence time of 0.8 sec, a flow rate of MeBr vapor of 12.28 sccm, anda total gas flow rate of 25 sccm. The main aromatic products weremesitylene, 49.3 wt %, and xylene, 23.1 wt %. Benzene production wassuppressed: 2.5 wt %.

Example 17 Catalyst Preparation of SAPO-34 Based Catalysts

A solution of 12.6 g of 85% phosphoric acid, 1.6 g of 37% HCl and 20.3 gof de-ionized water was added to 27.2 of aluminum isopropoxide in a PEbottle. The bottle was shaken for 1 min, after which 4.0 g of LudoxSM-30 (manufacturer) colloidal silica was added, and the bottle wasshaken again for 1 min. Then 56.2 g 35% TEAOH (tetraethylaminehydroxide) and 9.1 g water were added and the bottle was shaken for 1min. The mixture was then transferred to a Teflon-lined autoclave, andleft for 48 h under constant agitation at room temperature. Thecomposition of the resulting gel, expressed in terms of the molarratios, was TEAOH:Al₂O₃:0.89 P₂O₅:0.3 SiO₂:0.2HCl:64H₂O. The temperaturewas then increased to 215° C., and the mixture was heated for 100 h atthis temperature. After washing the precipitate with de-ionized waterfollowed by drying at 120° C. and calcination at 600° C. for 6 h, apowder sample was obtained. The pure SAPO-34 phase (CHA) was identifiedfrom XRD measurements. Partial framework substitution with metals suchas Co, Ni, Fe, Mn or Ga was conducted by mixing the individual nitratesalt into the starting mixture solution with a molar ratio ofmetal/Al₂O₃˜0.02.

Example 18 Catalyst Preparation of ZSM-5 Based Catalysts

Commercially available HZSM-5 materials with different SiO₂/Al₂O₃ ratiospurchased from ZEOLYST International were used as the initial materialsin this work. A representative example is CBV 8014, abbreviated here as8014. 8014 is an H-exchanged type ZSM-5 with a SiO₂/Al₂O₃ ratio of 80.The materials were modified by loading various metals via wetimpregnation starting from their salt solutions. The doped or exchangedmetals involves Mg, Ca, Sr, Ba, K, Ag, P, La, or Zn and the loadingamounts varied in the range of 0.1 to 10% by weight. The metal dopedcatalysts were further activated by calcination in the temperature rangeof 500 to 800° C. for 6 h prior to use. XRD patterns for the initialmaterial and the ones with metal doped were obtained to verify thecompositions. The loading of Mg or Ca slightly affected the peakstrengths but did not change the zeolite structures.

Examples 19

Some non ZSM-5 and non SAPO-34 materials such as ferrierite structurezeolite and a aluminophosphate (AlPO-5) can also be applied in theconversion of CH3Br to light olefin. These materials are eithercommercial available or were synthesized in our lab. AlPO-5 wassynthesized following the procedure described in IZA website with smallmodifications. The synthesis procedure is as follows.

(1) Mix 7 g water with 3.84 g 85% phosphoric acid

(2) Add 2.07 g triethylamine (TEA) drop wise to (1)

(3) Add 5.23 g aluminum isopropoxide to (2) in small amounts at 0° C.with intense stirring then stir the mixture at room temperature for 2 h

(4) Add 0.83 g 40% HF (in water) and 89.2 g water to (3), stir for 2 h

(5) Hydrothermal synthesis at 180° C. (preheated oven) for 23 h

(6) Wash the precipitate with DI water

(7) Dry the precipitate at 120° C. for 10 h

(8) Calcine the powder at 600° C. for 6 h

The XRD measurement confirmed that a pure AFI phase that belongs toAlPO-5 was obtained.

Example 20 High Ethylene Mode

High light olefin yields as well as high ethylene/propylene ratios canbe achieved by using narrow pore zeolite materials and conducting thereactions at elevated temperature. Two typical results were obtainedover SAPO-34 or CoSAPO-34 at 500° C. with 2.0 sec residence time and 0.2atm. partial pressure of CH₃Br. The CH₃Br conversion, combined C₂+C₃yield (C base), combined ethylene+propylene yield (C base) andethylene/propylene (weight ratio.) reached 91.4%, 61.9%, 58.7% and 1.7for SAPO-34 with 8.1% coke formation (C base) and 97.9%, 65.6%, 60.2%,1.7 for CoSAPO-34 with 11.7% coke.

A typical product selectivity and C mole yield for different productsobtained from SAPO-34 at 500° C., 0.2 sec and 0.2 atm CH₃Br are shown inTable 10.

TABLE 10 CH3Br Coupling over SAPO-34 at 500° C., 0.2 sec and 0.2 atmCH₃Br Catalyst, SAPO-34 Condition, 500° C., 0.2 sec, 0.2 atm CH₃Br C molSelectivity, % C mol Breakdown, % CH₄ 8.2 C₂H₄ 40.2 C₂H₆ 1.0 C₃H₆ 24.1C₂ ^(═) + C₃ ^(═) 58.7 C₃H₈ 2.4 other C₁-C₆ 16.5 C⁴⁻⁶ 6.5 BTXM+ 3.4BTXM+ 3.7 CH₃Br 8.6 RBr 5.1 RBr 4.7 Coke 8.9 coke 8.1 CH₃Br conversion,% 91.4 C₂ ^(═)/C₃ ^(═) (wt) 1.67 C Balance, % 100.3

Example 20 High Propylene Mode

High combined light olefin yield and high propylene selectivity wasobtained from ZSM-5 based catalyst at relative lower temperature, 400°C. and short residence time, <1 sec. The catalysts modified by loadingalkaline earth metals (e.g. Mg, Ca, Sr or Ba) show excellentperformance.

Using a ZSM-5 based catalyst with 5% Mg loading, 5% Mg/8014-750, 98.3%CH3Br conversion, 54.3% LO yield with ethylene/propylene weight ratio0.10 were achieved at 400° C. with 0.5 sec residence time and 0.1 atmCH₃Br. Much lower coke formation (0.6%) was measured compared withSAPO-34 based materials. The catalyst also showed excellentreproducibility during the test of over 20 cycles. The productselectivity and C mole yield for different products obtained using thiscatalyst are shown in Table 11.

TABLE 11 CH₃Br Coupling over 5% Mg/8014-750 at 400° C, 0.5 sec and 0.1atm. CH₃Br Catalyst, 5% Mg/8014-750 Condition, 400° C, 0.5 sec, 0.1 atmCH₃Br C mol Selectivity, % C mol Breakdown, % CH₄ 0.0 C₂H₄ 4.8 C₂H₆ 0.0C₃H₆ 50.5 C₂ ^(═) + C₃ ^(═) 54.3 C₃H₈ 0.0 other C₁-C₆ 16.5 C⁴⁻⁶ 29.3BTXM+ 3.4 BTXM+ 7.7 CH₃Br 1.8 RBr 6.9 RBr 6.8 Coke 0.6 coke 0.6 CH₃Brconversion, % 98.3 C₂ ^(═)/C₃ ^(═) (wt) 0.1 C Balance, % 92.1

Example 21 Moderate Ethylene Mode

High light olefin yield, >50%, flexible ethylene and propylene fractions(ethylene/propylene weight ratio, 0.3 to 1.3) can be achieved either byusing SAPO-34 and ZSM-5 based catalysts independently at a widetemperature condition or by using the two types of materialssequentially. Initially, the feed was allowed to contact SAPO-34, wherehigh ethylene/propylene ratio and incomplete CH₃Br conversion (70-80%)were achieved, and then let the product gasses pass through the secondcatalyst bed where highly active ZSM-5 based catalyst was loaded, whichsubstantially consumed all unconverted CH₃Br and produce more propylenethan ethylene as a compromise. As a results, a high CH₃Br conversion andacceptable ethylene/propylene fraction can be achieved from this mixedcatalyst system. It is expected that this combinational method still haslarge room for further improvement through optimizing the conditions forthe two catalyst beds.

From a sequential mixed catalyst system SAPO-34 B+5% Sr/8014-750, theCH₃Br conversion, light olefin yield and ethylene/propylene ratiosreached 93.3%, 51.7% and 0.7 respectively at 475° C., with 2.1 secresidence time (2.0 sec over SAPO 34-B and 0.1 sec over 5% Sr/8014-750)and 0.2 atm CH₃Br.

One typical result obtained from SAPO-34 B+5% Sr/ZSM-5 are shown inTable 12.

TABLE 12 CH₃Br Coupling over SAPO-34B + 5% Sr/8014-750 at 475° C., 2.1sec and 0.2 atm. CH₃Br Catalyst, SAPO-34B + 5% Sr/8014-750 Condition,475° C., 2.1 sec, 0.2 atm CH₃Br C mol Selectivity, % C mol Breakdown, %CH₄ 7.3 C₂H₄ 22.8 C₂H₆ 0.7 C₃H₆ 32.1 C₂ ^(═) + C₃ ^(═) 51.3 C₃H₈ 3.0other C₁-C₆ 20.4 C⁴⁻⁶ 10.7 BTXM+ 8.6 BTXM+ 9.2 CH₃Br 6.6 RBr 6.3 RBr 5.9Coke 7.8 coke 7.3 CH₃Br conversion, % 93.3 C₂ ^(═)/C₃ ^(═) (wt) 0.71 CBalance, % 100.9

Table 13 summarizes more results on the three operation modes.

TABLE 13 Summary of the Results for Three Modes of Operation: (1) Highethylene, (2) High Propylene, and (3) Moderate Ethylene Temp/ LO Yield,C₂ ⁼/C₃ ⁼ Coke, C-Balance, Mode Catalyst C. (sec)^(τ) PCH₃Br Conv. % %(wt) % % High C₂ ⁼ SAPO-34 500 2.0 0.2 91.4 58.7 1.7 8.1 100.3 CoSAPO-34500 2.0 0.2 97.9 60.2 1.7 11.7 100.4 High C₃ ⁼ 5%Mg/ZSM-5 400 0.5 0.198.3 54.2 0.1 0.6 95.6 Moderate SAPO-34 475 2.0 0.2 88.1 54.2 1.3 7.699.9 C₂ ⁼ Co-SAPO-34 450 2.0 0.2 96.2 50.6 1.0 10.8 98.3 CoSAPO-34 4752.0 0.2 96.8 58.4 1.3 9.9 99.8 Mixed 475 2.1 0.2 93.3 51.7 0.7 7.3 100.9Catalyst* *SAPO-34-B + 5%Sr/8014-750 (1.55 g + 0.1 g)

Example 22 Ferrierite

A non ZSM-5, non-SAPO-34 materials, with 2-dimensional and 10-ringferrierite structure was tested under the conditions for couplingreactions. A commercial available ferrierite, CP914 (Zeolyst) withSiO₂/Al₂O₃ ratio of 55 was tested at 475° C., 0.2 atm CH₃Br with aresidence time 15 of 1.0 sec. The catalyst exhibited moderate activitytowards the reaction and moderate ethylene selectivity. The CH₃Brconversion, light olefin yield and ethylene/propylene ratio reached49.8%, 14.8% and 0.89% respectively. The results are shown in Table 14.

TABLE 14 CH₃Br Coupling over Ferrierite at 475° C., 1.0 sec and 0.2 atm.CH₃Br Catalyst, ferrierite (CP914) Condition, 475° C., 1.0 sec, 0.2 atmCH₃Br C mol Selectivity, % C mol Breakdown, % CH₄ 10.9 C₂H₄ 13.9 C₂H₆1.1 C₃H₆ 15.8 C₂ ^(═) + C₃ ^(═) 14.8 C₃H₈ 3.4 other C₁-C₆ 18.0 C⁴⁻⁶ 20.7BTXM+ 3.9 BTXM+ 7.9 CH₃Br 50.2 RBr 14.9 RBr 7.4 Coke 11.4 coke 5.7 CH₃Brconversion, % 49.8 C₂ ^(═)/C₃ ^(═) (wt) 0.89 C Balance, % 99.9

Example 23 AlPO-5

Another non-ZSM-5 and non-SAPO-34 type zeolite, AlPO-5 was synthesizedin the lab following a procedure described on IZA website. XRDmeasurement confirmed the existence of one dimensional AFI structure inour sample. The coupling reaction was conducted at 400° C., 0.2 atmCH₃Br with a residence time of 2 sec. The catalyst gave 8.8% CH₃Brconversion with light olefin yield of 1.2% and ethylene/propylene weightratio of 0.62. The results are shown in Table 15.

TABLE 15 CH₃Br Coupling over AlPO-5 at 400° C., 2.0 sec and 0.2 atm.CH₃Br Catalyst, C-H-5 Condition, 400° C., 2 sec, 0.2 atm CH₃Br C molSelectivity, % C mol Breakdown, % CH₄ 13.7 C₂H₄ 7.9 C₂H₆ 0.0 C₃H₆ 12.8C₂ ^(═) + C₃ ^(═) 1.2 C₃H₈ 0.0 other C₁-C₆ 1.1 C⁴⁻⁶ 5.9 BTXM+ 0.9 BTXM+15.4 CH₃Br 94.3 RBr 1.2 RBr 0.1 Coke 43.0 coke 2.5 CH₃Br conversion, %8.8 C₂ ^(═)/C₃ ^(═) (wt) 0.62 C Balance, % 96.8

Example 24 Effect of Reaction Temperature Over SAPO-34

The coupling of bromomethane was conducted over SAPO-34 in a temperaturerange from 400 to 500° C. It was found that high temperature favors theformation of ethylene and propylene. It was observed that increasing thereaction temperature significantly enhanced CH₃Br conversion, lightolefin yield and the ethylene/propylene weight ratio. Coke amount alsoincreased from 4.0% at 400° C. to 8.1% at 500° C. At the temperaturehigher than 475° C., CH₃Br conversion exceeded 88%, light olefin yieldreached 55% or higher and the ethylene/propylene weight ratios werehigher than 1. Examining the product selectivity, it was found that hightemperature may promote C₄ decomposition, suppresses C₃H₈ and RBrformation and as a result, produces more ethylene and methane while withless C4 product formation. The results are shown in FIG. 33 and Table16.

TABLE 16 Effect of Reaction Temperature on Product Selectivity overSAPO-34 Catalyst, SAPO-34 Condition, 2.0 sec, 0.2 atm CH₃Br C molSelectivity, % 400° C. 425° C. 450° C. 475° C. 500° C. CH₄ 1.3 2.1 3.24.8 8.2 C₂H₄ 19.4 24.3 29.7 34.4 40.2 C₂H₆ 0.3 0.4 0.6 0.8 1.0 C₃H₆ 39.335.9 32.5 27.1 24.1 C₃H₈ 7.0 5.2 4.8 3.6 2.4 C⁴⁻⁶ 14.0 13.3 10.4 9.6 6.5BTXM+ 2.8 4.4 3.7 3.1 3.7 RBr 8.9 9.1 9.2 7.9 5.1 Coke 7.0 5.3 5.9 8.68.9

Example 25 Catalyst Stability and Reproducibility

The stability of the catalyst system for at least 10 cycles includingreactions has been demonstrated with SAPO-34 catalyst. Reactions wererun at 475° C. with 0.2 sec residence time and 0.2 atm. partial pressureCH₃Br. Catalyst regeneration (decoking) was done at 500° C. overnightwith 5 sccm air. The catalyst showed excellent stability andreproducibility in terms of CH₃Br conversions, light olefin yields,ethylene/propylene ratios, coke amounts etc. The results, as a functionof cycle number, are displayed in FIG. 34. No noticeable catalyst decaywas observed under these conditions and no structure changes wereobserved in XRD measurements.

Example 26 Effect of Residence Time on Product Distribution Over 5%Mg/8014

Using the catalyst of 5% Mg/8014 we investigated the effect of residencetime by changing the residence time from 0.1 sec to 5 sec. The data,displayed in FIG. 35 show that short residence time (<1 sec) favors theformation of light olefin while longer residence time lead to more BTXand light alkanes (propane and butanes), which contribute to the majorcomponent of “other C₁-C₆”.

Example 27 Methanol to Light Olefin Comparison

Methanol coupling to light olefin (MTO) experiments were also conductedwith two GRT catalysts, 5% Mg/8014, and 5% Ca/8014 and a commerciallyavailable MTO catalyst (Grace Davison olefin Oultra). Reactions were runat 400° C., 0.1 atm. partial pressure MeOH and a residence time of 0.5sec. The results are summarized in Table 17. The GRT catalysts havehigher combined ethylene+propylene yield.

TABLE 17 Comparison of GRT catalysts and Grace Davison C.A.O.C forConversion of MeOH to Light Olefins at 400° C., 0.1 atm. MeOH and 0.5sec Catalyst Utilization C₂ ^(═) + C₃ ^(═) C₂ ^(═)/C₂ C₃ ^(═)/C₃ 5%Mg/8014 93% 47% 100%  97%  (7/40) 5% Ca/8014 87% 51% 100% 100%  (3/48)Olefin Oultra 95% 37% 100%  85% (12/25)

Example 28

In order to demonstrate the above expected results, a lab scale setupwas used for bromination reaction. Typical bromination reactionconditions of about 500° C., 60 sec residence time, 70% CH₄ conversion,1.5 sccm O₂ was run for about 2 hours. The product gasses passed throughthe Ba(OH)₂ solution to precipitate CO₂ generated during bromination.After the first reaction cycle, the inlet portion of the reactor appearsclean, while the portion disposed downstream of the NiBr₂ bed appears tohave accumulated coke. The coke deposited downstream of NiBr₂ wasdecoked in the second cycle by switching feed directions. Here the cokefrom the bottom portion (the downstream portion in the first run) wascollected after removal of the NiBr₂ from the reactor. The measurementsof the amount of coke are shown in FIG. 36. The results indicate thatmost of the coke oxidized in the first cycle during bromination. Thetotal coke measured in this configuration appears to be greater than anempty tube bromination (based case), which may be due to CH₂Br₂conversion into CO₂ during bromination in the presence of oxygen.

The invention has been described with references to various examples andpreferred embodiments, but is not limited thereto. Other modificationsand equivalent arrangements, apparent to a skilled person uponconsideration of this disclosure, are also included within the scope ofthe invention. With reference to FIG. 1 and FIG. 2, in an alternateembodiment of the invention, the products 25 from the bromine generationreactor are fed directly into the bromination reactor 3. The advantageof such a configuration is in eliminating the bromine holdup needed inthe flash unit 27, thereby reducing the handling of liquid bromine.Also, by eliminating the bromine scavenging section including units 26,27, 31 and 34, the capital cost for the process can be reducedsignificantly. For energy efficiency, it is desirable to have the outletof bromine generation be equal to the bromination temperature. Forbromine generation, cerium-based catalysts are therefore preferred overcopper-based catalysts in this embodiment, since cerium bromide has ahigher melting point (722° C.) than copper (I) bromide (504° C.). Thepresence of oxygen in bromination and coupling reduces the selectivityto the desired products; therefore, the bromine generation reactor mustconsume all of the oxygen in the feed. In this embodiment, themonobromide separation 5 must be modified to remove water using aliquid-liquid split on the bottoms stream of the distillation column 51.The water removed in the liquid-liquid split contains HBr, which can beremoved from water using extractive distillation (see, e.g., FIG. 9),and then recycled back to the bromine generation section.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. While compositions and methods aredescribed in terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps. Allnumbers and ranges disclosed above may vary by some amount. Whenever anumerical range with a lower limit and an upper limit is disclosed, anynumber and any included range falling within the range is specificallydisclosed. In particular, every range of values (of the form, “fromabout a to about b,” or, equivalently, “from approximately a to b,” or,equivalently, “from approximately a-b”) disclosed herein is to beunderstood to set forth every number and range encompassed within thebroader range of values. Also, the terms in the claims have their plain,ordinary meaning unless otherwise explicitly and clearly defined by thepatentee. Moreover, the indefinite articles “a” or “an”, as used in theclaims, are defined herein to mean one or more than one of the elementthat it introduces. If there is any conflict in the usages of a word orterm in this specification and one or more patent or other documentsthat may be incorporated herein by reference, the definitions that areconsistent with this specification should be adopted.

What is claimed is:
 1. A system comprising: a coupling reactorcomprising a coupling catalyst for receiving an alkyl halide stream andcontacting at least a portion of the alkyl halide stream with thecoupling catalyst to form a product stream comprising higherhydrocarbons and hydrogen halide; a separator unit for separating atleast some of the product stream from the hydrogen halide; and anoxidation reactor comprising an aqueous solution comprising a metalcapable of forming multiple stable oxidation states for receiving asource of oxygen and at least a portion of the hydrogen halide from theseparator unit and generating a corresponding halogen and water.
 2. Thesystem of claim 1 wherein the metal capable of forming multipleoxidation states in the oxidation reactor comprises at least one metalselected from the group consisting of: Cu, Fe, Sb, Mn, V, As, Ru, and acombination thereof.
 3. The system of claim 1 wherein the aqueoussolution in the oxidation reactor has a pH less than about 7.0.
 4. Thesystem of claim 1 wherein the oxidation reactor is at a temperature fromabout 65° C. to about 300° C.
 5. The system of claim 1 wherein theoxidation reactor is at a pressure from about 0.1 atm to about 40 atm.6. The system of claim 1 wherein the oxidation reactor comprises atleast one reactor type selected from the group consisting of: acontinuous stirred tank reactor, a plug flow reactor, a packed columnreactor, a fixed bed reactor, and a fluidized bed reactor.
 7. The systemof claim 1 further comprising a product separator for receiving theproducts of the oxidation reactor and separating the correspondinghalogen and the water.
 8. The system of claim 1 further comprising ahalogenation reactor for receiving a halogen stream and an alkane streamand generating the alkyl halide stream.
 9. The system of claim 1 whereinthe halogen is bromine.